There's real UX benefit to it is why. Things instantly changing to entirely different layouts takes time to process visually, if things lerp to their new positions then that processing time is cut down to the length of the animation, which are usually around a quarter of a second, not half or a whole. It might get in the way of speedrunners and power users, feel free to disable them, but you're not the target audience. It's the average user who doesn't have every UI nook and cranny burned into muscle memory.
It's a nice theory but it only works if the animations are smooth and designed to improve understandability. The vast majority of UI animations are pure visual flourishes that take twice as long as they should and don't make any kind of sense spatially or physically or improve the user's understanding of what's happening at all. There's a lot of cargo cult UI design out there.
And what's worse is that most of the animations either don't start at the initial state of the UI or finish at the final state, or perform so badly that they hardly show any frames in between, so you have the worst of both worlds: abrupt jerky transitions and wasted time.
UI transitions that make spatial sense, are fast enough, are fluid, and don't slow down typical use of the UI are rare unicorns.
I unfortunately 100% agree. While an amount of whimsy should be everywhere, animation shouldn't be used as just eye candy. Like every other aspect of UI design, it has to be used with purpose and care. And yeah, that's way rarer than it should be.
Funny. I've had people hovering over my shoulder comment how my PC is so much faster than theirs when it was actually an RDP session to another PC, which seems to disable almost all window animations by default.
