The big difference w/playing from the arm vrs. the wrist is endurance. You will have much more endurance playing from the arm (obviously, the muscle is 20x the size of the wrist).
If you have ever listened to fast Be-Bop players like Pat Martino or Jimmy Bruno you will understand the importance of this technique. These guys are picking every note, playing VERY fast, and taking 2-4 min solos. Jimmy Bruno has a whole book out on the art of picking. http://www.jimmybruno.com
A lot of rock guys will pick from there wrist. They are usually playing shorter phrases, shorter solo's, and doing more hammer on/ pull offs & string bending.
Average length of a rock solo 20yrs ago: 20 -30secs.
Average length of a rock solo today: 0 secs.
[Edited by chris mood on 03-03-2003 at 10:59 AM]