[huttdes]

I understand the concept of that for Kodi knowing which files they are but once you get your artwork you shouldn't have to download any more so I don't really understand why its necessary

How are the website providers of the artwork going to know which fanart of theirs you have downloaded, if you have renamed all of their artwork? Right, they aren't, so they will see you have no artwork with their names, so they will download it again. Image how much extra bandwidth that will take up on their end, not to mention all the extra fanart you will now have. 

Maybe I'm not understanding something here or I'm doing something wrong.
I'm actually in the process updating all of my metadata and artwork.
Going through each movie one at a time and seeing if I need to update or add to my artwork. Selecting specifically which artwork I want... since all of them are not worth having.
Download what I need and batch rename the files.
That movie is now done... never to need anything downloaded again...