I guess it’s not typical use-case.
When emptying trash ( through Nemo, not through trash-applet so not the same as Trash applets : freezes whole desktop while emptying? ) all desktop becomes unresponsive and ends up by logging out.
Before it logs out, the deletion process had no effect on some running applications : I could still use Firefox or Thunderbird for example. But panels and desktop were totally frozen.
I said not typical use-case because I had something like ten thousands .png files ( thumbnails ) in the trash so I expected some slow down eventually but not the session logout ! Those thumbnails were not « in use » though.
What else ? Those files sit on a partition of an SSD disk, if of any interest, in the root of /home/$USER.
Any settings or attentions to care when deleting thousands of files ? A kind of buffer ?