What is capacity in OnCreateManager

I've been digging into the new ECS system and there is one thing that I haven't been able to find any documentation on. In the startup code for any system the signature looks like this:

Code (CSharp):

1. protected virtual void OnCreateManager(int capacity);

Looking through how this is called, it seems a world can set a capacity variable for each type of system, with the default being 10.

However I cannot find what the intention of this variable is? Is anyone aware of how this is intended to be used?