I've used it for several-month periods on several occasions to prepare for exams. In each case, once the exams are done, I would certainly like to have some broad recollection of their content (especially a feel for what sort of knowledge exists in the relevant field and how I might go about seeking it out again) but I don't care about it at the detailed level that I needed for the exams, and therefore that I put into Anki. (Anki works best for detailed stuff anyway, I find.)

I'd quite like to pick up a more long-term Anki habit where I only add stuff that I do want to know long-term, but haven't got round to it I guess. I'm not sure where would be a good place to start without a specific goal.