Consolidating itunes libraries into one
In that case, open i Tunes on your Mac and choose Preferences.
Then click on Advanced and look for the heading i Tunes Media Folder location.
https://appleinsider.com/articles/18/03/05/how-to-free-up-your-macs-internal-storage-by-moving-your-itunes-library-to-an-external-drive Conceivably there is a minuscule speed difference between i Tunes retrieving data from your Mac's internal SSD and an external hard drive, but as long as the music or the video plays, you don't notice.
It's possible, for instance, to have media that is listed in your i Tunes library but actually, physically resides somewhere else.
You should know whether you've ever figured out how to do this or if you've got any such media, but we're talking a decade and a half of using i Tunes, nobody remembers this stuff.
Apple keeps everything, all of your media and all of the information about it, in the one i Tunes folder so as long as that's safely backed up, it can be safely restored.
If you don't have the room for these duplicates on your internal drive, the default location that i Tunes uses, there is something you can do about it. You don't just run out of storage space through this duplication and consolidation.