Ethernet above drop ceiling — plenum cable “just in case”?
The purpose of plenum rating is that if the wire is overheated (e.g. from fire), it won't emit chemicals which will blind, stupefy, poison, or incapacitate people trying to escape from aforementioned fire.  This matters in spaces where air is handled. 

Maybe a drop ceiling won't be air handling space unless a duct is damaged, but consider the probability of the duct damage and the overheating of the wire being caused by the same event.