Filling your space only stops new uploads to the cloud until you free some or move up a plan; nothing is deleted to make room, and syncing between your own devices carries on. You can only end up over the limit if it shrinks under files already stored, for example when a paid plan ends. Then nothing changes for 30 days, and we email you twice. If you are still over after that, the most recently added cloud files move to your cloud trash until you are back under. You can restore them from there for as long as your trash keeps files (30 days unless you change it). Files on your own devices are never touched.