Ideally, you do this tuning experimentation with some old sheets that will not kill you if you mess up the job. It is good experience and discovery.
For all those who get butt-painz when opponent is a tuner, have it any way you like. I do not tune my Karis, it doesn't need it (I would bet that H would be a beast tuned) it works perfectly fine for me without tuner. Besides, re-doing that stuff every month or two is too inconvenient for me. Kinda fun to test out how the stuff works on an old rubber, but for main rubbers, too much work for me.
If my opponent uses a tuned rubber and saves money, moar power to him or her. I am not going to get offended and run to the referee to cry foul. That tuner won't help opponent read my serves any better or move his feet better or be on balance better.