I find myself faving an observation first due to its beauty. If there is a really pretty Buprestid, I’ll fave it. (https://www.inaturalist.org/observations/35289083)
I’ll also fave if the observation is rare, new, or significant to the iNat or general community. (See iNat’s only Acmaeodera robigo https://www.inaturalist.org/observations/11265477)
Third, if I myself particularily enjoy the observation for whatever reason, I’ll fave. (https://www.inaturalist.org/observations/35511517 The picture is not great, nor is it the first time this species has been posted. However, it happens to be my 2nd favourite insect, and I can’t help by fave every time I see one.)
Fourth, if the observation is significant and I want to come back to it, I’ll fave it. Most every time, this has to do with time or knowledge, in which I know I’ll figure it out, but I can’t at the moment. (https://www.inaturalist.org/observations/7136891 where I found the ID 6 months later, but would have killed myself searching through all the observations manually.)
Finally Gerald (https://www.inaturalist.org/observations/5890862)
All in all, I fave quite a bit, but don’t find a use for separating different categories of faves. It is not particularly difficult to scroll through the faves, and it can also be fun to do so :). There is no set in stone definition of faving, so no one is breaking any rules by faving an observation ‘incorrectly.’ The most I would want to be changed is possibly a way to easily sort through faves by taxon or location or RG/Needs ID similar to the personal observation page.