During the last stage of the charging cycle - the charger is balancing the voltage between the internal cells.
When you use the battery - it may discharge one cell faster than another so if you don't charge the battery before each use, you run the risk of over-discharging one of the cells which would permanently damage the battery.
If you use the battery every day - or several times a day - a good habit is to recharge the battery after every use. So you'll be all set for the next session.
If you don't use the battery every day, you must only recharge to the storage voltage until you're ready to use it - and then charge to the maximum capacity just before use. See the charging in formation for your specific battery by clicking the appropriate link below:
Charging Home Original 11.1v battery
Charging Home Plus 14.8v Battery
LiPo batteries do not need to be fully discharged before recharging, see: Recharge Before Fully Discharging - YES!