Just wondering what the difference between storage charge and normal charge and why is it so important to keep batteries in storage charge if not in use?

Storage charge is usually between 3.75-3.85v per cell where as full charge is 4.20v per cell.
Not storage charging a battery and leaving it at either full charge or low charge will reduce the batteries life span and performance.

You can always just make sure your packs are charged to around 3.8 volts per cell before you put them away. My charger has a balance charge function but I very rarely ever use it.

I: (a) run a fully charged pack a little until they are around 3.8V per cell or (b) balance charge the pack until it reaches 3.8V per cell. I always check my pack before putting them away by hooking them up to the charger and do either option (a) or (b) depending on what my charger says the voltages are.

There are little devices that you can plug your pack in to that give you a per-cell readout. They are relatively cheap- around $15.

Hope this helps!