Third comment in this post about this from me, but I've done university work while lucid dreaming, solved bugs we didn't even know existed, stuff like that. I don't think you rest as much while lucid dreaming, I'm pretty sure I built up fatigue at many points in my life just due to how much lucid dreaming I was doing. I now avoid lucid dreaming, and have started losing the ability to do it frequently (which frankly is a blessing). I feel more well rested now than I did when I lucid dreamt a lot. No way this idea doesn't just leave you completely tired after a while.