That is great video. Excellent, in fact,
The two reasons for motion that guy mentions is more detailed but he cannot go into in a short video, no doubt he knows. They could be subsets of motion, I guess
There are really four goals for motion
1. He mentioned one -- changing the strength. Move a player from the 3x2 formation it becomes 2x3. or 4x1 can turn into 3x2. THis is called "structural motion".
2, Then there is motion that is called "informational" motion. This is the classic "man" or "zone" thing everyone talks about but there is more to it. It can also serve to identify pressures, fronts (you can see the line shift left or right) and even more
3. If a motion is to make it easier for a blocker, (back or receiver) or to get a WR into space -- this is "advantage motion" the video talks about it a lot. Gettin a wide receiver in better spot to run route, to break the leveral of a defender.
4. Then there is traffic motion. That's meant to challenge the defenses' eye disciple and also to create traffic for defenders
That guy knows his stuff.