There is a notation called Tablature for guitar. Most of the keyboardists I have seen, use the staff notation.
Is staff notation useful for guitarists?
Will it help the guitarist in learning guitar?
A guitarist will benefit from learning staff notation. Depending on music style and ambition level, this benefit will vary. For someone starting out, I would recommend to try to learn staff at the same time. It is the common written language of music, after all. There will be vastly more material available compared to tabs.
That being said, the notation isn't as good match for guitar as for piano, and it is quite hard. Sight reading guitarists are a rarity for a reason. But you need to learn some of the staff notation for the rhythm, so it can't hurt to try and pick up the other stuff as well.
To summarize: Knowing staff notation is a benefit, so try it. On the other hand, a great host of guitarists has managed to do fine without it, so it's not something one is expected to know.
If you want to play classical guitar it is obligatory.
If you want to play jazz, it is VERY preferable.
If you want to play rock/pop in a garage, you'll survive without it.
In the end, if you want to be a professional musician, knowing staff notation will make you much more competitive, to say the least.
Staff notation is important for guitarists, once they have mastered it. The trouble with tab is that it doesn't tell the timing, unless, of course, the proper stave is there as well. It also tells where the author has played it, or thinks it should be played. This is very subjective, unless it's produced by the very same person who played a particular solo that you're trying to get.Many solos/tunes can be played in several different places on the fingerboard - I prefer to make my own decisions.
If you think you may end up playing in a reading band, or be a session guy, reading dots is probably essential.If, later you want to play another instrument, tab won't help at all - unless it's bass guitar...
If lack of timing marks is not a problem, 'cos you know the tune, why would you use the tab anyway ?
Another problem I find, as a teacher, is that so many downloaded tabs seem to be made by people still wet behind the ears, so are just inaccurate.
On the other hand, so to speak, tab can be invaluable to distinguish things like slurs - is it a bend up, slide up or hammer-on? Not available in standard notation - just shown as 'slur'.Harmonics, etc. Open strings as opposed to fretted - sometimes an important piece of information for the player. So, having both is the best solution, as they complement each other. One on its own is probably not actually sufficient. But that means to get the best out of it, you need to be able to read BOTH !!
Tablature is idiomatic notation, i.e. a style of notation that is specific to a particular instrument, and it can be useful in communicating information that is specific to an instrument.
It's particularly useful for guitar in that the guitar is a relatively difficult sight-reading instrument. Much of the sight-reading difficulty guitarists face stems from the simple fact that virtually any note on the guitar can be found on multiple strings. Well-written tablature can clarify what positions one should use to execute a particular passage.
That said, because it is idiomatic notation, it also has limitations. Staff notation is a remarkably efficient means for conveying a lot of musical detail in a small space, and it has the advantage of being applicable to any non-transposing instrument without modification. Compared to staff notation, tablature is actually fairly difficult to sight-read in performance situations.
So, yes, it will be useful in learning the guitar, but, if your goal is to be a working musician, you will need to learn to read sheet music, as you will almost certainly find yourself in situations where tablature is either not available or not ideal for the situation.
Personally I find the classical notation ill suited to a guitar, and while I understand it for playing piano I find it hard to use for the guitar.
However, it does provide some key information that most tabs do not - the rhythm is perhaps the most important of the things that are missing. Most official published scores will provide both the classical notation and a tab. I use the tab to find out what to play, and the classic notation to determine to rhythm.
This has suited me fine for 20 years, and may well suit you, depending on what you want to do with the instrument. I like to play blues and rock and jam with my friends. If you are learning Classical guitar and want to play in an orchestra I would recommend that you learn the staff notation.
Violins and other string instruments are no different re having multiple note locations.
Disagree with kiprainey that guitar is not suited to sight reading, it's an education thing - and most people learn to read tab instead. It's taking the easy way out, and it has been continually successful because there is less demand for session musicians who can read than the number of able guitarists out there. Chicken or egg? It's stupid anyway, and I don't think anyone in their right mind should encourage tab, or discourage classic notation.
Learning to read (classic notation) is something every musician should do, regardless of instrument.
Scrowler's answer is on the money. Staff notation is the standard way of reading music and applies to every instrument. It is the only way in which music is presented in professional contexts like the studio or bandstand. It contains much more information than tablature, allows one to play music written for other instruments, allows one to communicate with other instrumentalists in the written form. As for apparent difficulty, this is indeed a matter of education. For the most part, classically trained guitarists have no problems reading. It is those without a formal education which focuses the appropriate amount of time on learning to read that have a hard time. The argument that, it is too hard on guitar, is woeful. It's like saying that reading a foreign language is too hard and therefore a waste of time.
I'd say need is a subjective term in this case.
It's beneficial in that it helps you understand the language of music overall, it can be used as a medium by which most instruments can play. You give tablature to a piano player and they'll have no idea what to do with it, but sheet music they'll be able to understand a lot more.
On the other hand there are a handful of guitarists, like Jimi Hendrix, who managed to get by remarkably well without being able to read music, because they make up for it in musical ear, feel, passion, whatever you want to call it.
It's like language. You don't strictly need to write in order to speak it and understand, but for getting things down it's a very good medium.
So in conclusion, you don't need to learn staff notation, though it is highly beneficial to take the time to learn it.
Having the ability to read both types of notation is beneficial because of the wider ranger of sheet music that will be available to you. I often find it easier to read rhythm and chords when looking at staff notation. The downside of staff notation is that there isn't a one-to-one correspondence for a given note and it's representation on paper. Tablature eliminates this ambiguity and for that reason can make sight reading moving lines much easier (as long as adequate rhythm notation is provided). Ideally, both staff and tablature notation are provided when reading music. So yes, staff notation is useful for guitar if you take the time to learn it, but it is not a necessity to be a great guitar player. As far as staff notation helping someone learn to play guitar, I think it is. It helps a new guitar player to think of the frets as notes instead of numbers. However, as long as a new guitar player spends time learning the theory of music and how it applies to a guitar, this shouldn't be a problem.