My university used turnitin (I assume it still does), largely to check journal paper submissions and theses.

This was pretty frustrating, as my undergraduate thesis had some publishable work in it. When I reformatted the thesis up so that it would fit the standards of a journal, I still ended up getting a pretty high match...to my own work (the thesis). I ended up rewording as much of the paper as I could, but I couldn't get the %match below whatever the threshold was. Eventually my adviser said "ok, that's good enough" because he could see that I was being accused of plagiarism against myself.