"If you canceled your subscription to Apple Music or iTunes Match, your music library is removed on all of your devices except for the original computer where your music library is downloaded. Your iTunes purchases will remain in your Library on all devices. All music that you added or downloaded from the Apple Music catalog is removed. Any playlists added from the Apple Music catalog, created using music from the Apple Music catalog, or synced to a device using Sync Library are also removed."
So you cancel iTunes Match, your "cloud library" disappears. Meaning: Apple stops hosting your uploads and matches, but none of your local files are deleted.
If you ever want to turn it off, just make sure you've downloaded every song that shows as Matched or Uploaded so you’re not relying on Apple's copies. Then back them up somewhere outside your Apple Music or iTunes library folder to wherever you keep your full, DRM-free music collection.
https://support.apple.com/en-us/118287, "Do you have an active subscription to Apple Music?"
"If you canceled your subscription to Apple Music or iTunes Match, your music library is removed on all of your devices except for the original computer where your music library is downloaded. Your iTunes purchases will remain in your Library on all devices. All music that you added or downloaded from the Apple Music catalog is removed. Any playlists added from the Apple Music catalog, created using music from the Apple Music catalog, or synced to a device using Sync Library are also removed."
So you cancel iTunes Match, your "cloud library" disappears. Meaning: Apple stops hosting your uploads and matches, but none of your local files are deleted.
If you ever want to turn it off, just make sure you've downloaded every song that shows as Matched or Uploaded so you’re not relying on Apple's copies. Then back them up somewhere outside your Apple Music or iTunes library folder to wherever you keep your full, DRM-free music collection.