Part 1 is for a lot of the Same reasons Paul motioned his Abacks. Sets up multiple things within your offense, Counters, Sweeps, Tosses or in todays era (Touch Pass).
Part 2 is depending on how the defense reacts it tips their coverage or gives us a leverage advantage in the run game. There was a beautiful example of it that I recall against FSU. Can’t remember the time period of the game but Tech had trips to the field side with a tightend in the slot so four guys to the field side and they motion RB haynes to that side making it 5 of our players to the field, maybe to make it look like a set up a screen to the RB. pre snap FSU shifted a defender making it 5 on 5 to the field but also 5 on 5 on the boundary side, Tech makes FSU think play is going to the field but the result is every defender in the box was accounted for and blocked 1 on 1. Haynes looked left and scrambled right. All that presnap and eye candy for what was like a 6 yard designed QB run but that’s why they pay these guys the millions.