If you don't abuse your packs (i.e. discharge them at a higher rate than you should, or below the min voltage), then you can probably get away with occasional balancing. A few years back, balancing chargers were not as cheap as they are today, so I would just charge them, and check the individual cell voltage occasionally.

With the availability of inexpensive balancers and balancing chargers, it's best to invest in one to keep your packs balanced. I got  my balancing chargers from HobbyCity.com . Their Turnigy Accucell-6 is about $50 with shipping. That's a 50W charger that will do up to 6S LiPo packs. They also sell an adapter that will let you charge two 3S packs at a time on a single charger. I have two of these chargers with the adapters, and so I can charge (and balance) four 3S packs simultaneously. This comes in handy, since I have nine 3S 2200mAh 20C packs for my two Strykers.