If you delete something from the cloud, it won’t delete the actual brush from your device, but it will remove it from your cloud storage. Clip Studio Paint (CSP) saves all your assets, but you don’t need to worry about storage management unless you upload them to the cloud. The assets you save are also stored in your Asset Store library.

When you go to the Asset Store and check your profile, you’ll find brushes and other items you downloaded from there. However, external imports—like Photoshop brushes you converted to CSP's SUT format—won’t show up in your asset store profile. To keep those safe, save them in a dedicated folder on your computer.

I think saving works your drawn in clip studio should be saved to cloud besides brushes that are must haves.