Safest practice is to balance charge every time. This makes sure the cells don't go over 4.2 volts (or 4.35 for High Voltage packs), which can cause damage to the cells. You don't have to wait for the charge to completely finish every time if you are in a rush, as balance charging can take longer. Once the current drops below 1 amp for a typical 5000mah pack, you are 98% charged.