I have trouble finding any usecase for it. On the iPad it might be ok in some situations but so far I’ve been fine with a simple split view if needed. And that’s not permanent like Stage Manager.
On the Mac I don’t understand at all why it exists. We already have overlapping windows and spaces, what else would I need?
Apple was not able to explain to me why this was made. Feels like a hobby project by a young developer who imagined a new way of dealing with windows.