This did two things for me:

1. Extra strength in hands and forearms makes you more resistant to injury of all kinds there

2. More importantly I think, having extra muscles in your hands and forearms gives you more proprioception feedback to help know when you're putting your hands and wrists in an uncomfortable position.

I've read a lot of accounts over time of people who get to full RSI injury stage without realizing their hands were in an awkward position at their desk, but I've never had that problem because my forearms are meaty enough that any odd position pulls a bit on the muscles. I can literally feel when my hands are out of position, so every time I sit at a different desk setup, or change my chair position, I push my keyboard and mouse around until they're all kinds of angled and spaced away from each other and I feel no strain. I also regularly mix up hand/elbow position throughout the day because I can feel strain happening earlier in the muscles before it becomes a problem for my tendons.

IANAD, YMMV, etc - but I've been typing/gaming many hours most days for almost two decades and I've yet to experience RSI (knock on wood).