0.15 release notes: Bubbling observers section is confusing

[rparrett]

https://bevyengine.org/news/bevy-0-15/#bubbling-observers

Virtually every pointer interaction (like mouse click) is rare (humans are slow!), and often requires a complex response.

This pattern is particularly useful in UI, where unhandled interactions are often intended for the pane that contains the entity that's on top, but is also valuable for in-game interactions: clicking on a unit's sword should select the unit!

It feels like there's a missing sentence here or something. I am not understanding how the first and second paragraphs relate to each other. Also, I am taking the word "rare" to mean "doesn't happen nearly on every frame" but that leap required a bit of headscratching.