RE: prop balancing
With all due respect to the Pro's on this forum, I always balance my props to reduce vibration to the airframe. I also balance my spinners. As da Rock pointed out, vibration can do some funny things to screws and bolts not to mention electronics. Also, I never sand on the prop to balance it, I use a little spray acrylic on the light side. If it needs more than that I just toss it. Any nicks or cuts to the prop and it hits the garbage. I know I sound a little obsessive and I do have to admit that I go through more props than most people. I'll accept a lot of cosmetic imperfections on my model but IMO engine and flight control systems must be maintained to the strictest standards. My 2 cents.