Like most position groups in the NFL, receiver corps and those who coach those receivers have learned adaptation and versatility are the most important concepts in the modern game. You will hear coaches and executives say it over and over—the NFL is now a matchup league.
How can an offense gain an advantage over a defense? Put your 6'4" No. 1 receiver in the slot and let him lord over that 5'10" slot cornerback. If you're playing a team that likes to run a lot of single-high safety looks, force it to change its tune with pick-route concepts out of double-slot formations.