Using SimpleLogin with a custom domain vs using an email provider?

[pushkin-]

Can someone help me understand why I would use SimpleLogin with a custom domain vs using a custom domain with an email provider like Tuta or Proton?
I could create email addresses with my custom domain and link it with Tuta, say. Is there an advantageous to using SimpleLogin for this? Is it just that I can have it generate random email addresses for me?

Right now, it seems to me like I should just prefer creating aliases with my email provider / domain registrar and then I can control all of that from there and only use SimpleLogin when I want a randomly-generated address that I can throw away later (though I suppose I could enable catch-all for this as well)