No use being snarkey ...... I sure don't know more than GM engineers but I do know they help improve air flow through the engine compartment at highway speeds and do little in low speed driving such as in city type traffic. We are talking about working trucks and towing duties.
Radiator fans were once controlled by engine rpm now most are done electronically.
Low speeds/low engine rpms/city traffic the fans work as engine temps rise such as sitting in traffic or pulling a trailer up a steep grade.
Get out on the highway at high speeds and the fans shut down as the air flow increases.
A google has lots on the subject of the lower air dams on our trucks and what they do.