Real case: a dev machine's npm-cache had grown to 11.4GB. Cleaning gives temporary relief (it grows back) — permanently relocating the cache path is the actual fix.
Is deleting the npm cache risky?
No. The cache is just copies of downloaded packages — after deletion the next npm install re-downloads what it needs, slightly slower once.
Why do I have two npm cache folders?
Older npm used %AppData%\npm-cache (Roaming); newer versions use %LocalAppData%\npm-cache. Machines that upgraded Node often have leftovers in both — both are safe to clean.