I think it's more about preventing user error. It's easy for legitimate apps to suddenly start recording on laptops/desktops when you're not expecting it. One

I think it's more about preventing user error. It's easy for legitimate apps to suddenly start recording on laptops/desktops when you're not expecting it. One example is when you're waiting for a video conference to begin, you don't want the camera to suddenly turn on when you're not ready for it. I like there to be an explicit action before I allow recording. For smartphones there's a permission model where I have the ability to explicitly grant permission every time an app wants to turn on the camera. However such a stringent permission model doesn't exist on desktops/laptops, so a slider is a simple low-tech solution to the absence of a sufficient software permission model.