Simply put, low gears can lessen the chance of injury as your giving yourself more mechanical advantage And thus lowering the stress to your body and joints.
Something I did myself. I kept pushing to hard too soon. I was young NEW and didn’t know any better. Torn meniscus in my knee. Not a bad injury and healed fairly quickly. But it was an annoyance and I learned from it. Now that bike had lower gears I just was trying to push too hard a gear for the trail conditions. This was rider error. Something else more prevalent in newer riders.