Less time + less matetrial + Less work = higher profit.
We have done 1000's of full soles this year. Not one 1/2 sole.
Ask people in the shoe industry which would they prefer on their own shoes, 1/2 or full soles?
They will tell you full soles.
I normally suggest that when the worn area of the heel gets down to about the thickness of a dime it's time to replace. This way the customer gets the most use out of a pair of heels without damaging the base.