Some URL shortening services allow users to see very basic information on who has clicked-through the link. If I remember right, it documents the visitor's web browser, computer's OS, exact date and time of click-through, on what site they clicked on the link or whether it was manually typed in, and sometimes a very rough approximation of geographic location. I realized while rewriting my resume and submitting graduate school applications that if I replaced all the links to my portfolio with a shortened URL, I would be able to see if and when my applications were being reviewed. Since I was applying to departments all over the country, I would very likely even be able to tell which department was viewing my materials.
I ultimately did not do this since I was of two minds whether it was ethical. On the one hand, I could see an argument for it being an advanced application strategy since one should assume websites are already tracking this info; on the other, I could see a department seeing this as unwarranted snooping and a breach of privacy adjacent to hacking. What's more, I know that if I was better at web development, I could set up my portfolio site to track most of this information automatically. Is this ethical? Is it enough of a grey zone that I can still use it? Does it make a difference whether I am applying to a university or a private sector job? Does it make a difference which department I am applying to?