I did a lot of stuff with brickOS when it was still legOS. I started out in NQC, but it just wasn't fast enough. I had a two-wheeled robot that did dead reckoning by counting wheel revolutions to figure out where it was in the room. NQC took about one second per navigation update. My robot was kind of hilarious running NQC, because it would jump forward and then stop for a second while it calculated the navigation update, then jump forward and stop again, etc.

Using native C, I got the navigation update cost down to 10ms, allowing for smooth driving without having to stop and wait for calculations.