My threat model is company tracking. I feel like I stand out like a red target with a random letter username, but it's just so companies using tools like Sherlock will struggle to connect my other accounts. I found it exhausting to create new usernames that I liked for every service.
I've actually been wanting to create a normal fediverse account self hosted with my own domain, but I haven't done it yet because I haven't completely determined what I want to do yet.