When I coached, one of the things I wanted was offensive linemen who at least played all offensive line positions in practice as much as possible. The objective wasn't as much as to find out which positions they played best even though it did shed some light on it. The real reason was that I wanted all my linemen to totally understand the assignment of each and every lineman on every play as it was called, so they were aware of not only their responsibility but that of everyone else because there were a lot of plays where they could help out on a blocking assignment or pick up a block missed by someone else. I appreciated the average player who followed those roles more than the player who could make pancake blocks but only focused on their own responsibilities. They were showy but they weren't necessarily the guy you wanted to count on when the script flipped on you during a play.
In skull sessions, I'd spring questions on the linemen. I'd ask a left guard what the responsibility of the right guard and tackle were on a play, even when it was totally away from their area. Questions like this would catch them off guard and they studied the plays to ensure they knew the right answers and could carry out the assignments themselves if thrown into that mix.
I didn't just know to do this. I was taught how this worked when I played HS football. A coach who made my life less difficult as an RB by having linemen who carried out their assignments. As it is, I took a lot of hits, and in my era, it was really the Woody Hayes philosophy of; "Three yards and a cloud of dust." But to my coach, it was 4.5 yards and punish the defense for trying to stop the play. I'd be battered and bruised after 25 to 30 carries in a game, but I never experienced a major injury because our line was always moving bodies and nobody was able to get clean shots at me. Getting 125+ yards in a game was consistent and I don't think I was tackled for a loss more than 20 times over 4 years of carrying a football. But it wasn't me. I probably wouldn't have been able to play on a large city team where speed alone was their forte. I survived because of the blocking, and we won games we probably should have lost because he knew how to control the game by running the football. I was just a tool for his plan.