What's the point of the USP-RPS if it doesn't also have a battery?

This specifically: https://store.ui.com/us/en/products/usp-rps
Like, I get that any of the UniFi device's internal PSU could die and that the USP-RPS would take over but the whole thing just feels like a lot of cabling and cost for something that's not very likely to happen.
Or is it just assumed that the USP-RPS would be connected to a UPS battery backup and then you are using it as power distribution?
Can you even run devices off the USP-RPS without ALSO connecting their AC power cables at all? Negating the need for each device's AC cables would at least maybe simplify things?
I'm still really surprised UniFi hasn't come out with a real UPS - especially because even if I use an APC/Eaton/TrippLite/etc then it's not like it communicates with the UniFi gear.
So, what am I missing - it just seems like such a weird product.