Could be helpful if it silently (or at least subtly) warns the user that they're approaching those boundaries. I wouldn't mind a little extra assistance preventing those embarrassing after-the-fact realizations. It'd have to be done in a way that preserves privacy though.
Like most scientific and technical advances, it could be an amazing tool for personal use. It won’t, of course. It will be used to make someone rich even richer, and to control or oppress people. Gotta love humanity.
Definitely a hazard. My ideal solution is something that could be built and evaluated in a way that allows me to know that it does what it's supposed to do and nothing else. From there, I'd want to run it on my own hardware in an environment under my control. The idea is to add enough layers of protection that it'd be easier and less expensive for that authority to change my behavior by hiring goons to beat me with a wrench. At least then I'll have a fairly unambiguous signal that it's happening but getting to that point would take a significant investment of effort, time and money.