Regarding the picking up of white slips: Sometimes it is a case of "you don't know what you don't know."

Maybe the individual drops trips they don't like and then WS to fill in their schedule. They may be, for various reasons, below the GS trigger. Or maybe they want a certain type of trip/report times/etc. etc. and can't usually get a GS or don't want to wait/hope for one that meets their criteria.

A friend of mine is constantly dropping trips/swapping trips and picking up new ones via WS to fill in his schedule.

Who knows. Lots of different variables to make any sort of blanket statements regarding it.