Straight line speed helps you a few big plays per game and occasionally it opens underneath routes, but quickness helps you almost every play either directly or indirectly via the running game. That is why receivers like Beasley get roster spots. They are short and not overly fast either due to natural limitations or their height's impact on their stride span, but they are very quick and shifty. When you watch some of the game's best tall receivers and then see a short slot receiver on the field make a play, you think that short receiver is so fast when in reality, the tall receiver would likely beat them easily in a straight-line 40 time.
That is something else that is great about watching football. There may be "prototypes" for positions, but there are always exceptions and alternatives that are fun to watch. We saw it this last year at quarterback with RG3 and Wilson. I like that some teams mix it up with their roster to combine both big and fast with short and quick skill players. It helps make games more interesting and provides a good balance that keeps defenses from all migrating to the same style of defense and types of players.
/reality
