Flight tends to be a force multiplier.
The basic functions of a combat unit are to shoot, move, and communicate.
Flight allows the movement part of those functions to be multiplied into an entirely new plane of movement. Through that, the others are likewise enhanced.
Does that matter in 5E D&D?
I'm not sure. In general, the game approaches combat in a very different way (and with a very different mentality) than other games I play.
I still believe that flight acts as a force multiplier, but at this point it's somewhat lost among options which grant greater power to PCs.
I think something overlooked is that hold person (and other options mentioned upthread to counteract flying) doesn't work on a faerie PC because they're not humanoids.