The third base coach provides some help to runners when the ball is behind the runner. However, the first base coach does virtually nothing. In 2009 MLB required that these on field coaches wear batting helmets after a minor league coach had been killed in 2008. Hey, they shouldn't be out there in the first place.
The best base runners coach themselves anyway: see Derek Jeter and Willie Mays.
It might even speed up the game. I always wondered why the batter and base runners did not simply look into the dugout and get the sign directly from the manager or a surrogate. Of course, it would be even better if MLB used wireless communication, like the rest of humanity.
Get those coaches the heck off the field!