Do not delete files directly from
C:\Windows, DriverStore, WinSxS, or Windows\Installer just because they are large.
Quick system-file answers: Do not manually delete pagefile.sys, WinSxS, DriverStore, or FileRepository. These are the system-file topics currently getting search impressions, so start with the linked guides before deleting anything.
Common large system files
hiberfil.sys
Hibernate, Fast Startup, and C drive space.
pagefile.sys
Virtual memory and why manual deletion is wrong.
Hibernate vs Sleep
Which power mode uses disk space.
Large Windows folders
Windows.old
Delete only when rollback is not needed.
WinSxS
Clean the component store safely.
Windows Installer
Why manual deletion can break apps.
Drivers, restore, and indexing
DriverStore
Driver packages and why they are protected.
Device Driver Packages
Disk Cleanup category vs protected FileRepository folders.
System Restore Space
Manage restore point storage carefully.
Search Index
Reduce indexed locations instead of deleting blindly.