Storage
System Data
Storage used by caches, logs, Time Machine snapshots, virtual memory and other system files.
What it is
In System Settings › General › Storage, System Data covers everything that doesn't fit the other categories: caches, logs, local Time Machine snapshots, swap files, developer tools data and more.
It often grows after heavy use and shrinks on its own as macOS cleans caches and expires snapshots.
Should you worry?
Only if it keeps growing and your disk is nearly full.
What you can do
- Restart, which clears temporary files and swap.
- If you use Xcode, delete old simulators and derived data from within Xcode.
- Give macOS time: it removes local snapshots and purgeable caches when space runs low.