Somebody please explain what, other than the game actually being simulated, is happening in these two spins that is different?

Are there certain things that have greater impact during the Mid-Week spin than the Game spin, for instance?

Midweek is there for roster movements. Say you have 53 players and 2 QBs are injured and you need to sign an additional QB .. this is the the spin to sign them and then release a player (to get back to 53) before the game spin.