To learn all the modes, and over what progressions they can be used, is very good. For most rock and blues tunes, you can get along pretty good with the good ol' pentatonic scales, but to learn the modes opens up more of the fretboard. It makes it possible to play more interesting solos, both for rock, blues and jazz tunes. It may not sound very nice with a pentatonic over a maj7 chord, for example. For those maj7 and 7-5 chords, lydian and locrian modes can be good to learn. The moxolydian mode is one of the most common used ones, used over the dominant 7th.
Now that i've written so much, it would take too much space here explaining the modes and scales. Checkout:http://www.guitarplayers.net/lessons/lesson08/lesson08.html
There you have a good explanation of modes and how to use them.
Hope it helps you