The problem with self portraits is they can seem vain. But the main reason people do them, I think, is to experiment and try things: either you wouldn't want to waste time with a model, or you just don't have a model handy.
It may be why photographers, and painters for that matter, have so many pictures of their younger kids, posed so artistically.
Kids are handy and you can pop them into the set and ask them to stand this way or that. Until a certain age, they are fairly obliging. Later, it's more of a cajoling game. Till finally they tell you to pound salt, or words to that affect.
That's when the self portraits start in earnest....until the grandchildren arrive!