I have done an unthinkable and read the manual

on tablespaces. And I have stumbled on something that I can not find an explanation for and hope that you guys can help me out here. here is what I found.
This topic can be found in: Administration Guide: Planning
If you need to drop and redefine a particular table often, you may want to define the table in its own table space, because it is more efficient to drop a DMS table space than it is to drop a table.
Question is:"Why is it faster to drop a table space with the table in it, then simply drop redefine a particular table?"
I know it got to be very simple, but I am drawing a blank on it.
Thank you in advance.