Really its the internal resistance of the pack.

The higher the C rating the more current can be pulled from the pack without damage. The lower the resistance the less heat that will be created during high current drain, hence, less chance of damage.

The downside is the higher c rated packs usually weigh a little more and cost more.


Something to keep in mind, manufacturers C ratings are often, shall we say, optimistic. Some mfg's are more like fantasy. So keep a saftey margin.