In the DMG there's a rules variant for rolling proficiency instead of using a static number... do you feel it's worth the brain space to calculate a variable each time instead of a static number in your head?

No i dont think its worthed and prefer a static bonus than a variable one.

When you're first learning to play, static is a must. I'd much rather a new player focus on learning and understanding the rules than having another step of the extra dice.

For more advanced players that understand the game, it's less of an issue. Still, the mechanics need to speed up rather than slow down, and while it's only a small slow down...it adds up and is heading in the wrong way.

I do think that 5e suffers for some of its simplicity. I'm not sure this method really helps though. I guess you get to use more clackety-clacks?

I struggle to see what the benefit would be. Less predictable outcomes? Incentivizing long-shot attempts at things..?

I've never used it because it doesn't seem useful.