Watch the Hammer Ons & Pull Offs online guitar lesson by Jeff McErlain from Blues Guitar Survival Guide - Lead
The classical name for hammer on's and pull offs is slurs. I think we often take these for granted but like everything if we take a closer look we can get more mileage out of them. A very obvious use is to play faster, picking every note of a line can sound cool but it is often impractical or we just don't have enough technique. Believe me, even the fastest pickers use slurs. They also smooth out a line to make it more legato. To practice these I recommend running through the pentatonic scales slurring as many notes as you can always with a metronome.