It's there so you won't lose 10mm sockets.
No reason, its trim, for looks.
Top of radiator has sharp edges.
Mine has been off for years, same with that plastic cover on top of the motor, just for looks.
Zero noticeable effect on cooling with scan gauge 2.
It's not necessary under most conditions. But under severe service like towing max weight on a very hot day up a grade, at altitude, it can help keep the coolant temperatures in check.
Personally I think it there for looks and to give the hood latch some slight protection from crud.
Some little strip of plastic is not going to do anything to adding cooling.
Some of these newer car motors are nothing but plastic cover mania when you pop the hood.