Why having a 'weak' hand is good, and why they may be better described as "support" hands

I suppose this is a result of creatures being unable to focus on more than one thing at a time. There’s no use in having two dominant hands because you’d never have any hope of writing two things simultaneously with each one. So the non dominant hand specializes in doing as much as it can without your focusing on it. The fact that you can have your left hand manage the position of what you’re working on subconsciously is impressive.

I’d be interested to see if left hands are better than right hands at performing idle tasks without our focusing on them.

When I was a kid, I was ambidextrous. I guess I am still (some tasks require me to sort of juggle which hand feels right), but it led to some issues with learning to write and shoot a rifle. I would try to write with either hand, and even submitted an essay backwards in second grade that I'd written with my left hand. I couldn't figure out how to hold a rifle because either way felt "right," but I was also cross-sighting (looking with left eye holding righty, or the reverse) because I hadn't quite developed the right coordination for it. I used to throw balls with either hand, as well. As I got older other stuff that was right-dominated just made sense, like guitar or using a mouse and keyboard.

I wouldn't be surprised if it was found handedness is a development for efficiency, as my general lack of it has led to many small stumbling points in my life. Nothing crucial, but occasional difficulties with new tasks as I have to settle in to a hand for a given task, rather than have a default.