They are for many reasons, the main one is to spread the defense which keeps them from stacking the box and blitzing more players. By not stacking the box it also helps the run game. It also helps from doubling Smitty as much if they have to account for another player or two.
What good are receivers if Cam doesn't have time to throw to them? OL and receivers WR/TE are far and away my biggest concern.
To often I saw teams being able to man up with our receivers, taking the ball carrier away, that leaves the Oline trying to not only block their man but two other unblocked defenders. You can upgrade the Oline all day but you will always be against the odds if you can't demand to spread the D.
No doubt we need an upgrade for the Oline, but I'm in agreement that the best help for the line is to actually upgrade the receivers.