Rotor and Stationary Gear Clearancing? ?

[FC Zach]

Back story:
About a week ago I sent my rotating assembly off to RB to have balanced and once received they called me back to negotiate what all I wanted them to perform. I told them that while they're at it I wanted the rotors clearanced and the bearings replaced with race bearings.

The guy there told me that both the stationary and rotor bearings will have to be clearanced.

So here are the questions:

-Race bearings for the rotors come in only one size, how will I be able to clearance them and they're replacing them, why don't they do it?

-I bought a RX8 E-Shaft and matching stationary gears, is it necessary that I will need to clearance these since they're new?

-Most importantly, what exactly is clearancing the bearings?