Ah okay! I can see the need for this. This is a large part of why the States machinery exists, but I see your point about it being error-prone to remember to tag and then despawn everything.
I'll chew on solutions here: we might be able to get away with a nice well-documented convention in user-space code, or we may need to add a small extension to the internals to make this more robust.
Isn't the typical way to do this by using a janitor? This would typically need to be done in user space (the framework doesn't know what cleanup you want to do), but Bevy could provide an interface for it with callbacks or whatever is more idiomatic in Rust/Bevy.
