I realised that in disk cleanup (cleanmgr.exe) there is an item "Thumbnails":
Windows keeps a copy of all of your picture, video, and document thumbnails so they can be displayed quickly when you open a folder. If you delete these thumbnails, they will be automatically recreated as needed.
I was pondering about why there is even an option to delete the thumbnails. Is it true that there will be "dead" thumbnails (for example if I delete a folder that has a thumbnail and the folder is deleted but the thumbnail still exists) so this option is used to clean "dead" thumbnails?