depening on how much you are using JD, its much more.

- JD\logs\extracting
- JD\cfg\archives
- JD\logs\updatehistory
- JD\tmp\update

there are leftover files which can get easily reach several thousand files. from my experience, above ~ 5-000 to 10.000 - depending on system - windows slows down on accessing such folders.

suggestion:
frequently scan JD folders for trash and delete them. updatehistory may be useful for debugging, but i think everything which is 2 month and older should be safe to delete.