When I play barre chords using jazz voicings such as in the following chord chart:
I often wrap my thumb around the neck to fret the E string. I prefer this, rather than using my first finger, as it makes it easier to play more complex chords since it frees up an extra finger. I want to know whether this is considered 'bad technique' and whether this has any negative long term effects on playing.
Using your thumb isn't "bad technique" per se. It's either appropriate or it isn't, given the context in which you do it. For example, if this chord is sandwiched between two others which require the first finger barre, maybe it would be better to leave the finger down through those chords.
Bad technique is what I did when I started playing years ago, saw Jimi Hendrix using his thumb, and decided I didn't need to learn how to barre properly!
Who has the power to decide? Any technique that works for an individual cannot be a bad one. Yes, purists may disagree, but it's not them playing, it's you! As stated already, an extra digit is always an asset, particularly on extended guitar chords. I'm only jealous, having small hands...
The traditional arguments against wrapping the thumb around to fret the sixth string are that it slows the hand down when you need to change fingerings, and that it brings the other fingers closer to the strings so they are more likely to mute other strings unintentionally. This matches my experience; but if you can play quickly and cleanly with your thumb wrapped around, those reasons needn't bother you.
I find that when I try to fret with my thumb, or even just have my palm on the back of the neck, my wrist and fingers are flexed more, and there's more tension in my hand. Even when playing a barre, my hand feels much more relaxed if I have only my thumb on the back of the neck. This make it easier to play for a long time without getting sore.
It is unorthodox, but it's not bad per se. I'd definitely recommend learning to barré properly/use your first finger too, and then use whichever is appropriate based on the specific chord and its context.
A classical guitarist (or at least, a classically-trained guitarist) wouldn't really use their thumb like that at all, but plenty of top guitarists still do: Metheny, (Jeff) Beck, Emmanuel, Hendrix, SRV, Bonamassa, etc... Loads.
I find it does produce a slightly different sound - somewhat warmer and fluffier than using your first finger. This is because your thumb is going to be quite flat against the neck, whereas your first finger would be more pointed (i.e. you would be using your fingertip more).
There are no downsides to this technique if applied appropriately. However, if used as an excuse to not learn other fingerings, you might find it limiting when playing chords that demand a full barré or similar.
So yes, it's fine, but learn to play it both ways and then use whichever you feel.
I wouldn't say this is a bad technique. There are many guitarists that use this one, for the very same reason you mentioned. You have one extra finger, thus you can play one more note. Also, when I play a chord like this, it is more relaxing for my hand.
Not at all, it's a great technique! There are chords that you can only play by using your thumb, e.g. the following voicing of A13(b9) (from low E to high e):
5 X 5 6 7 6
where you play the E string with your thumb. If you used your first finger to play a barre chord it would be very difficult to mute the A string.
Some of the tricks used in country music where the guitar was for show more than anything else, the would wrap their thumb around the three base strings and the index fingers around the 123 in same fret to form a chord. Then moving it up and down the neck the singer could play along with the band. Some of those country singers playing was worse than their singing. I use my thumb watch some of Johny Cash videos he uses the thumb
I play steel string acoustic guitar and I find that in many instances using the thumb to barre is actually more ergonomic than using the index finger.
Typical use case for using the thumb is when I want to play or mute the low EA strings while simultaneously playing or chording on the GBE strings on a steel string acoustic guitar. In this case if I barre with the thumb, then I can keep my wrist straight much easier and with less finger pressure than if I use my index finger.
YMMV, of course.
Try playing F#dim with your thumb on the bass string to get the correct inversion, and then it’s obvious that this one’s a no-brainer. Yes, it does slow you down so it should be avoided, but in certain circumstances it really opens up the instrument’s full potential by getting the correct inversion and using all 6 strings.
For starters, the chord you have given as an example isn't technically a barre chord; the "standard" fingering uses your four non-thumb fingers with no need to form a barre at all.
However, this doesn't really matter for your main question, which is whether it's bad technique to use your thumb to play notes on the low E string. Any experienced musician will answer any "Is this bad technique?" question with it depends, because bodies and instruments come in all shapes and sizes and there is always the possibility that an unusual technique will work perfectly for someone.
That said, there are a few reasons why using the thumb for these sorts of chords is not the default choice:
A13 voicing and the Dmaj7 voicing right next door. I bet that in this context, you will find the standard fingering to be more economical.In real life, many guitarists (including many who are considered to have "good technique") do use the thumb fingering. But they are more likely to use it for chords lower on the neck, since this gives the elbow more wiggle room and allows to to maintain a relatively straight, relaxed wrist position. The further up on the neck you go, the stronger the recommendation becomes; where you choose to switch from thumb to fingers will depend on your personal geometry. I have relatively small arms, so I find it comfortable to use the thumb fingering as high as the 10th or 11th fret, but after that I do tend to switch to the standard fingering for the reasons given above.
Another way to make the thumb fingering more comfortable and enable a straight wrist position when playing with the thumb is to hold the guitar with its neck pointing slightly forward. There is an Adam Neely Q&A video where he suggests this idea; I will add a link if I can find it.
If using your thumb helps you to reach notes more effectively then it can't be bad technique. If it slows you down doing certain things, then it is not good technique at that moment. BTW, I think you'll find that a generally cooler way to play that A13th is to play it without that low A anyway.
I think it depends what sort of chords you are transitioning to/from. For example, the thumbed-barre F chord would be and easier transition to/from a traditional C or a G chord than the non-thumbed F barre chord.
On the other hand, the “proper” barre chord is easier to maintain and move around further down the neck, especially closer to the 12th fret.
