I would say that if the pilot gives a full readback of the instruction and the controller listens to the readback properly then there is no harm in using whatever heading you like. I don't find the need to use degrees as I will always say "Turn left heading 180, descend FL150." So surely the "Turn left heading" versus the "descend FL..." makes it clear which is which. I understand that pilots who may not be fully switched on at the time may get them swapped around and thats why it is our job as controllers to listen properly to make sure the instruction is understood. Just my opinion.