It is important, and yes, you should invest in one. There are the finger tip balancers, too, which do an ok job (that's what I use 'cause I'm broke).

Balancing a prop saves tons of engine and structure wear by decreasing vibrations. People will say that props come pretty close to being balanced; I have yet to see one - every prop I've come across needed something (little sanding or addition of some clear acrylic).

Engines are expensive, balancers are not. They are a good investment.