Nope. These are just like the in-file ID3 tags in your MP3 files. They can be used to exchange metadata with other copies of MC, or with other applications. MC writes them, but doesn't actually use them unless it imports a new file with no information and it finds the sidecar file (or you manually tell it to "Update Library from Tags").
Video file types (particularly AVI) don't support tagging in the files, so MC uses these files (called "sidecar" files) to store the metadata. These can also be used to recover if you lose your library files in a catastophe of some kind.