My father did it when he was a child so he could "be like his brother" who was 1.5 year older and the favorite son of his mother (this brother was the first male son after a female who was the first overall).

He is now right handed for almost everything but really skilled with the left hand, I remember that once he broke the right wrist and could easily write with the left hand for example.

I have an older sibling who is left Andes and challenged me to use my left hand since they could use both. So I’m at about a typical left handed person’s level of dexterity with their right hand. I switch off on tasks like shoveling or sweeping. I can write badly. Etc. I wouldn’t say it is useful, really.

I mean, I'm here typing with my left hand.

Rafael Nadal, one of the best tennis players in history, supposedly is a natural righty who was taught to play lefty.