In the beginningI'm right handed, and, like most right-handed people, started off using my mouse with my right hand. Now, when I say I started off, I mean when I first used a computer with a mouse attached, which was certainly not the first time I used a computer. It was probably at least ten years later. So, by the time I started using a mouse I already had some computer use habits fairly well-established. Anyway, it felt natural to use the mouse with that hand.
Moving on ...
Scroll forward several years (at least two decades, so my mouse habit was well-established by then) and I noticed a colleague using his mouse with his left hand. I asked him if he was left-handed, and he told me he wasn't, but found using his mouse with the left hand was useful as it left his right hand free to take notes.
The more I thought about it, the more sense this made. I gave it a try and found I was very quickly able to learn to use the mouse with the "wrong" hand. Maybe this is partly because I am a bass guitarist, so using the left hand to do things other than just gripping was already something I did.
So, why does it help?
When I am working at my home office desk, my laptop is docked out of the way on a docking station in a slide-out drawer to the right of my working position and I use a wireless keyboard and mouse. I have my mouse on its mat to the left, keyboard in front of me and paper notebook to the right. So, when I need to take notes, I don't have to take my hand off the mouse (though I usually do) and, more importantly, I don't have so far to reach to get to the notepad. This is especially useful as I have the keyboard positioned with the "home" keys to the middle, which means I already have the number pad to the right of the main keys I use. Moving to a notebook past the number pad and a mouse mat would mean moving my hand something like fifty cm (18"), which would also mean either moving my chair or twisting around to write. It's not so much the moving, but the interruption it causes.
Why shouldn't you do it, and when don't I do it?
If you do a lot of fine work with the mouse, drawing, graphics, photo editing, etc., then it might make sense to use the mouse with your dominant hand as you tend to have finer control with that hand. Mind you, if you are doing a lot of that, you probably have a drawing tablet / pen anyway.
Interestingly, when I am using a laptop on its own, I don't usually bother connecting a mouse, mostly because it's just one more thing to carry. So I use the built-in track-pad, and that I normally use right-handed.
If I am doing a lot of writing, as I do when I am thinking things through, sketching ideas, etc. I generally push the keyboard away (benefit of a wireless keyboard!) and just use pen / pencil and paper.
What do you think?
Give it a try, let me know how you get on.