Let me start with IMHO, YMMV, and so on.
In my band days, when the guitarist would tune down to drop D, I might or might not, depending on the song. A few songs really benefited from the low D on bass, and some sounded just fine without it.
I got really good at tuning from E down to D and back again on the fly.
I felt like I really benefited from learning how to play in drop D; it got me out of my old pattern habits and made me think about what I was doing, more than I would have by tuning everything down a step.