It seems like the Baraag and Pawoo (I think run by Pixiv) instances both host very... uh... vibrant pornographic, and sex positive art communities, and it is convenient for those users as Tumblr banned them all, Twitter patchily bans explicit content periodically (JP users get a much looser leash than EN it seems) and DeviantArt forbids anything more explicit than artistic nudes.

I don't use it, mainly because I'm unclear of what the implications of choosing an instance are. I have a wide range of interests and I worry I'll be siloed if I choose just one.