Gammadoodler
Hero
Oh, I totally get what you're trying to do and I appreciate that thought process. And if these checks appear to be equitably distributed and adjudicated, (and used sparingly) maybe that's all right.It goes to RP.
Think back to Fellowship of the Ring. The Inn of the Prancing Pony. The bartender had to bend over the bar to see the hobbits. Or your other example - DEX checks for humans to avoid tripping over halfling-appropriate barstools.
Again, think back to the beginning of the movie. Gandalf bumps his head on a ceiling beam. This wasn't even scripted; it was McKellan accidentally bumping his head on the hobbit-sized set. Why keep it? Why have that flub? Because it established the size difference.
Would I have a halfling roll for every interaction in a goliath bar? Probably not. But there may very likely be one to add flavor - to establish that the character is physically out of place. Why would I make a centaur roll dice to traverse stairs? It's difficult terrain for him. He's not simply any other character who has a some bonus abilities. He's a character who is going to likely have difficulty interacting with some parts of the environment. It's one of the aspects of his Equine Build.
That said, there is a number of barstool or stair-related checks, beyond which I'd likely invite you to screw yourself.