I have guitar, the action is really high. My question is: what's the affect of learning and practicing in high action in the long term? Is this an advantage or not? Is high action something that'll keep me as an intermediate-beginner from moving forward?
How high is high? And what is the cause of the high action? If it is an improperly cut (too high) nut, it will make barré chords in the first few frets difficult, and open chords will be out of tune. If it is too high because of a bridge that is too high, or too much neck relief, it will be increasingly difficult to play the higher up the neck you are, as well as cause problems with intonation.
On the other hand, I can see how a high action will help a player develop hand strength, at the cost of slowing you down. A guitar with high action will also have better tone and dynamic range (this may be a subject of some debate) since the string has more room to vibrate and can be struck harder before "hitting the frets". (This mostly concerns acoustic instruments.)
All in all, if the instrument is playable, use it! But perhaps be on the look-out for a better one, or investigate the possibility of having the action lowered/corrected. Will it keep you from moving forward? Again, it depends on what you want to be able to do. At some point you will probably feel the need for a better instrument, but until then, keep on playing!
If the guitar is playable, then it shouldn't cause any major issues and may actually help build hand and finger strength. Unless it's so difficult to play that it results in excessive stress. If playing your guitar necessitates too much muscle tension to overcome the high action, playing it could potentially lead to over use/stress injuries. So it really depends on how difficult your instrument is to play.
It will slow your progress as you attempt to develop speed and add more barre chord formations to your chord vocabulary. But if it's temporary with an eye towards a lower action guitar in the future, it could help with your progress in the sense that you will be forced to adapt to greater challenges. It would be the same concept of an athlete training while wearing a weight vest. It would slow him/her down but potentially accelerate strength building by forcing the muscles to overcome greater resistance. But again - too much added weight could lead to injury.
I would encourage you to consider either having the action of your existing guitar lowered to a comfortable playable level or acquiring a guitar with lower more playable action fairly soon. As a beginner to intermediate player, you could become frustrated if the action of your guitar makes it difficult for you to play some things you want to play. My personal philosophy is that at the beginning stages, you want to make playing your instrument as easy as possible. You want the learning process to be rewarding and not frustrating. Later, a high action guitar can be used periodically to maintain and increase finger strength.
It depends on ergonomics and tone.
In general, you want your action to be as low as possible without string buzz; otherwise your intonation will be off, it will be hard to get strings to sound cleanly and you will do physical damage to your finger joints and also possibly get carpal tunnel syndrome. I'm speaking from experience here.
On the other hand, Stevie Ray Vaughan used thick strings and played with a very high action because he liked the tonal characteristics of his guitar when it was strung that way.
Yes! I practice with a high action cause I'm crazy like that! It definitely increases hand strength. But most of all, I love the sound of pressing hard and getting that nice Jazzy tone. I use .14 .18 .26 .26 .36 .47 .56 flat wound gauge. Nevertheless, I probably would play faster for up tunes with less tension. I have to have another guitar with lower action. Especially when I use my thumb like Wes Montgomery. When I play other guitars with lower gauge I can really rip, but it does depend on the guitar. For instance, I cannot play comfortable with very low action. Maybe because I'm so used to the high action. On the other hand one "cat" plays with 12's on an Ibanez archtop. I can rip on that guitar. Now, you go figure!
My students still call me crazy Dave and my guitars usually need adjustments. My repair men always tell me I should stop putting heavy gauge strings with high actions. They could be right, but I don't care. Play what feels good and sounds good if you like high action. But practicing Jazz chops! Go on and raise that action! Rock and roll chops and R&B etc... low action only! Might as well stick to your guns.