Hey, it wouldn't be normal for me to NOT argue with Ken and Minn, would it. [&:]

One problem with our judgement of model vibration is that we actually can see only the "slow" vibrations. And we often judge the balance of our props by what we see. And about all we'll see is the gross vibration. The difference in slow and fast is really frequency. The bad balance we see is low frequency. And it can obviously do bad things.

Bad thing is that the higher frequencies we don't see on the ground can bite the airplane in the air.
Bad thing is that there is a thing called damping. Why is it bad? Because when our airplane is running on the ground, we're holding it to the ground. Or holding it back. Whichever it is, the model has something that can absorb and damp.
And when the airplane is flying and all that damping has to shift out to other places, resonance and just plain "too little damping" can let the vibration change frequency.

So I've always felt it worth the effort to check prop balance, reject the bad ones, and balance the ok ones. That way, ain't no bad old vibrations gonna sneak by.

Also, one reason a number of people feel strongly that props don't need balancing nowadays can be that they don't see any out of balance when they do check. How many brands of props are there? Do we all use them all? And do some guys only use one brand? Or only use one type, like reinforced nylon? You know anyone who won't use wood because they break too easily?

Recently, I ran into a number of APCs that came to rest at 3-9oclock INSTANTLY. Why? Hole off center toward 6oclock? Lead slug hidden in the hub at 12oclock? Lord, I don't know but those puppies made me pull out my old razor blade balancer and check to see if the newer balancer was messed up. The props were messed up, not my balancers. I took 'em back and went to the other LHS and bought the same sizes and found another APC out the same way. I took that back and avoided buying APCs for awhile. Recently purchased ones haven't done that trick again.

In the last year I've been keeping a rough count of how many of each type and brand show badly on the balancer. Not a hard study, just making a mental count. And I'd guess about half the wood props I've bought get thrown into the pile to be balanced. And maybe one or two out of 10 synthetics get set aside. And I haven't needed to take back a synthetic since that run of APCs. And have seen no real difference in counts by brand.

How off can a prop be to make me work on it? If it is very SLOOOWwww to move, it's ok as is. If it WHACKS around, it goes back into the bag to go back to the LHS. In between gets worked on.

............................. If you're a beginner, it would be to your advantage to buy a good balancer when you can afford it. And your own testing will do you a world of good in making your own decision on this. It will also help you get a handle on the advice you get on the internet.