Operating systems need free space to work. They use the drive for temporary files, virtual memory and update staging, so a drive above roughly ninety per cent full makes everything feel slow, including tasks unrelated to storage.
The good news is that most of the recoverable space is not personal data. Update caches, old restore points, browser caches, application temp folders and downloaded installers routinely account for tens of gigabytes.
Photos and video are the other half. Cloud sync often keeps a full local copy of everything, which quietly doubles storage use on a laptop with a small drive.
Work from largest to smallest and check before deleting. A tool that shows folder sizes finds the real culprit far faster than guessing.