What are: /Users/<username./Library/Caches/Adobe/Lightroom/Video/Media Cache Files for?

I found these files by accident and wonder if its safe to delete them all. The file names relate to music-song titles and individual photos that have been used in LR-generated slideshows going back for several years. Looks like a waste of hard dive space to me. !  Despite having all of these cache files, slideshows take a very long time to generate themselves. Shouldn't the cache files delete themselves at some point?

Tech environment is LR 5.7, Mac OSX 10.8.5 on a desktop iMac.

THANKS!