How does the library work?

I'm trying to understand how the asset management works in Roll20. I have this layout: Premium Assets   Marketplace Purchases Cozy Cabin Map Pack 2019 Dastardly Demons ... Subscription Sets Free Assets 0 - Freebies 01 - Characters ... My Library Eberron: Rising From the Last War Character Art Pack Essentials Kit Character Art Pack ... Recent Uploads Token 1 Token 2 ... I'm about to upload a bunch and want to lower my quota. If I delete from Recent Uploads, is it gone forever? Like, I was just going to mass delete (slowly, by clicking on things one at a time in the Recent Uploads pop-out folder :() things, but then I started to wonder... Can I accidently delete something from "01 - Characters" permanently, or is it there for good? Does it count against my quota? How about from "Eberron: Rising From the Last War Character Art Pack"? I think I saw some stuff from that under "Recent Uploads", but I have no idea why that's there... I didn't purchase it or upload it, IIRC. I'd like to keep it though. What does copying from Premium Assets to Library do, quota wise? How about copying to a Folder? What's the difference? It is very confusing.

Anything in the Premium Content tab doesn't count against your quota.  Anything in My Library does, so if you copy something from Premium Content to My Library, it will count against your quota.  The folder system in My Library is more like tags to organize your assets than an actual folder system.  If you delete something from a folder you created, it is still on your account.  If you delete out of Recent Uploads, it removes it from your account, removing it from anywhere the image may be in use (maps, tokens, handout images, etc.) and lowers the amount of data against your storage quota. If you have uploaded music, that also counts against your storage quota (sometimes people forget about that and wonder where all their storage went).

Thanks! So... why would I want to copy from Premium to Library then? Just for organization?

It would make a difference for API scripts. The API can manipulate objects in a personal Art Library, but not those in Premium or Marketplace Purchases.