I think is fine if you just count the browser,OS, and country the user is from but I don't think is OK to keep more details then that
Now that I think about t I’ve never used analytics for anything ad related.
Everyone's been sucking up all the data they can just in case they need it, and actual people are being harmed by it through data breaches. I get why people are upset about these changes happening to their businesses, but what did everyone expect when the industry has failed to self regulate against their worst excesses? The rest of society isn't just going to let you hurt them so you can make more money
Using that data as well to improve learning so we do a better job of detecting fraud and not flagging legitimate customers appropriately.
Also, using analytics to determine if a user is having issues on the site. For example, are users having a difficult time filling out forms, or becoming confused, and being able to provide help in an appropriate manner.
These are just two things I immediately thought of. Security, and customer support. I'm sure there are many other users of analytics aside from ads and ad-tech.