Windows accumulates cache files, crash dumps, old update packages, and temporary files from dozens of applications. Most of it is safe to delete. Some of it isn't. Here's the breakdown.
Safe to delete
Windows Temp (C:\Windows\Temp): temporary files created by installers and system processes. Nothing here is needed after the process that created it finishes.
User Temp (%TEMP%): same idea, per-user. Some apps leave gigabytes here.
Prefetch (C:\Windows\Prefetch): launch prediction files for applications. On SSDs these provide no meaningful benefit. Safe to delete; Windows recreates them.
WER crash dumps (C:\ProgramData\Microsoft\Windows\WER): Windows Error Reporting accumulates crash dumps. Unless you're actively debugging a crash, these are just eating disk space.
Delivery Optimization cache: Windows Update downloads updates and caches them to share with other PCs on your network. This can be several GB. Safe to delete.
Windows Update log files: C:\Windows\Logs\WindowsUpdate. Pure logs, no functional data.
Thumbnail cache: Windows caches thumbnails for File Explorer. If you delete it, thumbnails are regenerated on next view. Safe.
Browser caches: Chrome, Edge, Brave, Firefox, Opera all cache website assets locally. Deleting them causes pages to reload assets on next visit — no data loss.
Game launcher caches: Steam Web Cache, Discord cache, Epic Games cache, Battle.net cache — all safe. Largest ones are usually Discord's GPU cache and Steam's web browser cache.
Leave alone
C:\Windows\System32: obvious, but some "cleaners" scan here. Don't touch it.
WinSxS: Windows Component Store. Cleaning it requires DISM /Online /Cleanup-Image /StartComponentCleanup, not manual deletion. Manual deletion breaks Windows Update.
Driver cache (C:\Windows\System32\DriverStore\FileRepository): removing these makes it impossible to reinstall the driver without a fresh download.
PageFile and hiberfil.sys: these look like large random files. PageFile is virtual memory. Hiberfil is the hibernation file. Delete hiberfil only if you explicitly disable hibernation first.
Automating it
IzanagiOP's Cleaner has 100+ individual targets — all of the above, plus app-specific caches for Spotify, Roblox, Minecraft, Valorant, Teams, Logitech G Hub, and others. Every item is individually selectable. Discord: https://terweb.lt/
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