A lot of it is to make teams adjust their alignment which will give the offense a chance to call plays based on the adjustments. Does the DL shift to gaps, LB's slide, etc. A lot of Iowa's run game is based on body count. People always rag on Iowa about changing to a run to the boundary, but it's all about count. For example, if we have 5 bodies to their 4 on that side, the play may get changed or if the numbers aren't in our favor, a play may get changed (not necessarily at the LOS, but in future calls to that motion). That's just one example. It's the same with post-snap "motion" with a jet sweep motion to see what the defense does to account for it. I'm guessing something Iowa saw made us run it more than most weeks.
The other thing is to see which pass defense a team is in. If someone follows motion, it's man. If not, it may be zone. If it's zone based on a certain motion, we can call plays to attack that zone. If it's man, we can use certain motion to get matchups we want or get an area to our advantage (to run a rub, get one particular receiver with a favorable matchup on an island, etc).
Other things could be to simply set up tendencies to break them later, such as motioning a FB or TE to load up a side to run behind.
Against different defenses, there are a lot of reasons to use motion, so I can't say exactly why all of the motion was used. As much as so many will disagree with me, BF really does know what he's doing (some do it better than others, though). There's a lot more to it than just looking at a play sheet and randomly calling something. People say we have such a simple offense, but there's so much more to it than thinking we're seeing the same plays over and over again.
By no means does this all apply to Iowa or the Iowa/NW game, just general reasons teams use motion. I've been a HS DC for 25 years and the more I know, the more I realize that I don't know much at all, so I'm positive there are many more intricate reasons for using motion.
