I balance every prop I get..... test it yourself.... take a prop, don't balance it, don't even test to see how out of balance it is and put it on the plane... start the engine and throttle up.... feel the plane... now shut it down, take the prop off, balance it and do it again...
Then you decide....

Yes I have seen some props (1 to be exact) that was sufficiently balanced out of the box, the rest? Anywhere from off to WAY off... personally I do not want something that is spinning in the neighborhood of 10,000+ rpm out of balance....