Hi Paul — I’m the author of Mole.
The main culprits are mostly unglamorous things: app and system caches, logs and temp files, old browser leftovers, developer tool caches, and remnants from apps that were already removed. On macOS these can quietly grow to tens of gigabytes.
Mole focuses on cleaning only those categories and does it conservatively. It’s rule-based, blocks critical system paths outright, and offers dry-run previews so users can see exactly what would be removed before anything happens. The goal is to remove accumulated junk without risking system stability.