Delay isn't a tactic that most would use, especially those fond of "rocket tag." Delay's primary value is in occasionally setting up real world tactics that can't work under 5E's initiative system. Realize that unless you roll initiative for each monster individually, you're allowing them this ability while denying it to players.
I don't think Dex is the god ability score, yet I allow the option to delay. Since 5E came out, I've seen it happen maybe 3-4 times, usually because two players wanted to set up something together, but an enemy could move between their turns and ruin it.