I’d say I go two ways with how I handle my usernames. On accounts where I post my art, interact with my friends and people I’m oomfs with I go by either Twiggie or Twigz0n, or just Twig. Twigz0n and Twiggie are both nicknames based on my online alias Twig, which is how most people know me online. I’d say this is my main I guess lol
I have one side account where I post things like personal artworks, sketches or miscellaneous stuff where I go under a slightly different username. It’s mostly a privacy thing and because I don’t want everything I do to be tied to my main art accounts, especially when the artwork or things that I post has themes or subject matter that don’t fit with what I usually post. It’s also more of an organisation thing too, as I don’t want my gallery to be a mix of finished projects and miscellaneous doodles. (At least not anymore lol)
I also might use a different name for certain social media/websites where all I do is make stuff like playlists with music or videos, or make collections of other peoples artworks for inspiration. I just don’t really see why I would need to have my public alias tied to accounts where all I do is mind my own business mostly.