You can totally use it without having Recommendations. It is an out of the box feature of Target Standard. If you aren't seeing what you'd expect for "Category Affinity" targeting check out this doc on how it populates
I've used it on all types of mboxes from global, regional, and raw boxes and it has worked as I've expected. The algorthm that it uses to define favorite can be confusing, so if it isn't making sense you could reach out to CC.