1. Easier to see a player dropping passes, they want to know the things they can't see. Of course you can see a guy like Donald Jones dropping passes and know he isn't that good.
2. Lol if you don't perform in game you won't be on the field for long so this question really doesn't matter. Like I said with the first it is for everything coaches CANT see.
With both of your questions have nothing to do with the equipment since the coach can see all of those things that are wrong. If you listen to the video you can find out what the equipment is for.