When doing UI things, a common workflow is to have code and the app side-by-side, make a small tweak in the code, recompile/hot-reload, look at he result, repeat. A long compile time makes workflow a pain.

It's not as good as Flutter/RN hot reload but SwiftUI previews do make this a lot better.

In general, you're right. But there are at least 2 times where they're absolutely vital- anytime you're dealing with a UI and data exploration in data science (since you make a lot of frequent, small changes in the goal of fine tuning something.) Everything else, best practices has good testing and partial compilations to make it moot. There's probably some other contexts that make it valuable, but I've never had to deal with those.