I'm kind of new to the forums, but I've been visiting this site for several months now. Truly, lessons and tabs hosted here helped a lot in improving my technique, and made me learn to play guitar on my own without taking lessons (and making me feel great about it). Hopefully the database would grow for years to come

Anyway, to the point...

I've seen in several videos that some guitarists fix their index finger across a single or several strings while playing solos. Now, I never played a solo this way, and have no idea how useful this is. My idea would be that it's either used to mute the strings after playing a note, or generally giving the other fingers a better sense of where to go. Still, I'm not into the guitar playing as long to figure this out. Can anyone instruct me what this is? If it's really useful, perhaps someone would give me some tips on how to play in this manner?

i do that all the time. i started doing because i saw my heros do it but now i do it for different reasons. i just find its easier to go from string to string and doing hammer ons and stuff. i just think its a lot easier than having to "reset" your fingers every time you move down or up a string. i move around a lot so it helps to barre 2 or 3 strings. i usually like to play more than one string at a time as well so it works for that too.
I used to do that but the simple truth is it slows you way down. Not to say that you should never do it, for example a lot of blues cliche licks use a barred finer in order to let the notes ring toether and give a dirty tone. But if you aren't doing something like that you should never bar it, it slows you down and creates nasty feedback (for example try playing one of Hammet's cliche licks barred....it doesn't work).