There are a lot of good points in this post but the real crux of it all on what to play and when has quite a bit to do with your band line up. If you are the guitar player in a power trio, you will need to play all six strings more often than if you were in a band such as the dead with essentially three players playing in the same frequency range, guitar, guitar and piano. Notice how Bob and Jerry were always trying to play in different octaves or in different positions on the fretboard. I always look at bands and how they waste space by having two people play the same chord in the same position. For some bands however, they do this to add a thickness that maybe they want in their music. For me, I like to hear the entire frequency spectrum, which is why a lot of bass players I have played with ask me to play without rooting on the 6th string as sometimes it makes things a little bottom heavy. You find a lot of jazz bass players like this. Some people have made a good point about using the thumb for barre chords. Definitely an advantage. Hendrix was the master and it allowed him to always be able to add single note R and B fills with his chords. If you plant your index finger across the frets, it can limit you. The best point made was about learning the CAGED formula. Do this and understand what notes are where, know that for example in this position, the root is on top, or in the middle, etc. Know that a major 7th chord consists of the root, 3rd, 5th, and Major 7th. YOU MUST LEARN THIS STUFF!! DO NOT JUST LEARN THE SHAPES AND CALL IT A DAY!! Play triads all over the fretboard. Start with your basic D chord, then play D at the 5th fret, and then the 10th, etc. All of this will come in great use when soloing and moving between chords in solos. Watch footage of Jerry, he is always playing notes built around the triads of chords he plays which is why he can play scales all over the fretboard and makes it sound seamless. Nothing lamer to me then watching a guy play a G chord down at the open position and then have to suddenly shoot on up to the 12 fret to solo in G Major. There are lamer things but I was trying to make a point.