For some people, the height they wear there guitar is generally about comfort, or for some people, the superficial sense of looking cool.
You will notice some particular guitarists like Rusty Cooley, Shawn Lane and Jason Becker, to a name a few, wear their guitars high to very high. This is for a few reasons. One is that to play what they do, simply couldn't be done if they had their guitars low. Wearing it high provides you with more stretch capability. It benefits those who have a more than average length difference between the pinkie and index, middle and ring fingers than other people. You will see Shawn Lane, Jason Becker and Cooley perform so rather large stretches at times, like the one string diminished arpeggio common to Lane, on all strings. Even Zakk Wylde, known for wearing his guitar very low, will raise up his leg on speaker box or do certain stance that involves bending the right leg back a bit, and then with the knee on a right angle, or close enough to one, for certain solos and his solo spots, to achieve his use of single string diminished arpeggios, as the guitar is now on his left leg raised vertically, close to his body and higher up for his wrists.
Wearing the guitar high also increases stretches on the lower strings at higher frets, hence why Lane, Cooley etc, can perform large stretches on say, higher than the 10th fret on the low E/ B, in the case of Cooley's seven string, and play wide stretched pentatonics and single string arpeggios. And of course, playing the guitar high puts less strain on the wrists, and after a certain height, none or little can be felt.
But you ask, why some shedsman get away with the guitar low, like Paul Gilbert and Marty Friedman. Well I've noticed Paul Gilbert, is quite a lanky man, which of course adds to his humorous ways, but he seems to have perhaps longer than average arms and the way he angles his wrist when he plays, allows him to stretch more, which some guitarists can do, others cant. Marty Alsp seems to be able to angle his wrists in way. But again, a style examination, and Gilbert and Friedman don't use quite as "stretchy" licks as Lane or Cooley and in instances that I have seen paul gilbert playing wide finger licks, like on serrana arpeggios, he was sitting down.
Another big factor, is the scale length of the guitar. When I play a guitar with a scale of 25.5 inches, I tend to have the strap set very high up, because I play things like 3 octave sweep arpeggios and large stretches on the higher frets, like single string minor arpeggios and wide pentatonics. If I wear the guitar even slightly lower, I can still play those licks, but my wrist begins to strain, and like some teenagers like myself, I have skinny forearms and wrists still so I would imagine any pain is no good, other than callouses from bending. Any lower than that and the stretches simply become impossible for me and I'd imagine for many people. But putting on a 24.75 inch scale guitar, and I can comfortably wear it at only tiny bit higher than what, say, Steve Vai wears his guitar.
Always take into consideration your physiology when you strap a guitar on. Joe Satriani may play his guitar fairly low, but those same licks played at that height to me would cause me wrist strain, and could inevitably lead to injury, like carpal tunnel syndrome etc.
So if your concerned about whether you may strain your wrists, play your guitar at a height which will not cause you any strain and this inevitably means fairly high for most, and this goes out to all players, not just shredders or technical metal style players. If you are concerned about looking cool, and having to wear it low it means several things: one is that you are at peril of injury; you will have more difficulty playing sometimes perhaps, having to lean to the side to play chords or licks etc; Your audience is very shallow if they are concerned about superficial things such as the expectation of a low guitar, a problem with some rock and metal crowds, not really prominent for the shred and jazz audiences; and perhaps you are shallow as well about it. I'm sure the audience would want the best playing performance possible, and wearing the guitar higher can ensure that.
But of course consider that people like Clapton, and many rhythm guitarists in many poppier bands like say, oasis, don't have technical playing and certainly Clapton's or BB King's blues are not going to need wide stretches of todays virtuosos, and as such it would be safer to wear the guitar lower than Rusty Cooley and not be strained, but again, heed warnings.
Another good idea, is too play a guitar with jumbo frets. Jumbo frets not only give more sustain, but they make a guitar easier to play. They also encourage your hands to develop a lighter touch. I personally find jumbo frets to be easier on the left hand. A larger radius fretboard, 14 inches and above for me, make bending easier and wide vibrato easier, so once painful bends for me on rounded radius guitar with small frets, became a breeze when switching to Brian Moore Guitars and Jackson, the main guitars I use. Also, reasonably regular polishing of the frets can keep bending easier too.
I hope this article is useful for some, and bear in my mind this is my first contribution to UG. Please post comments about any points you think I may have missed or overlooked.