Usually practices are split up with one main facet being individual position drills (or, for example, QBs working on the mesh with BBs or QB/BB/AB/WR skeleton drills). Another main facet is scout team.
I think a lot of posters on here have misconceptions about what Scout team is. It is NOT a test of skills. It's NOT designed to be a 100% accurate depiction of the other team.
It IS, however, a test of knowing the scheme and the gameplan at 80-90% speed.
If you think our walkons without more than a week of practice can emulate teams like uga, VT, Clemson, UNC, FSU, etc. you're crazy. That's not the point. The point is, here's a play you are going to see Saturday. Are you in the right position? Did you cover your assignment?
It's more of an instance to work on the mental aspect of preparation. The skills part (tackling, running, getting off blocks or, in Vad's case, learning the offense) comes from the other aspects of practice.