I like to identify species from the county I live in and sometimes in places I have travelled, am familiar with, and like to see what observers have posted since my visit (or sometimes before I visit). I regularly use 2 filters: plants and unknown and try to id unknowns at some level. I never just use unknown. Some unknowns I can at least use course categories so that the previously unknown organisms show up on expertise searches.
From reading the replies it looks like many of us who use the unknown filter are strategic about it: curiosity, target geographic region or taxonomic group. I am appreciative of the filters and assisting others toward accurate id’s.