Honestly, it's all aesthetics.
The grill is efficient and doesn't block enough airflow to make a difference.
For that same reason, I don't think removing the grill makes a significant difference in protection either. It's so thin... unless the rock hits square on the horizontal part. lol.
Those plastic pieces behind aren't load bearing, they don't really do much other than to be there for the grill to clip on to.
If you don't care about keeping the car reversible (to go back to oem one day), then just cut those plastic pieces for a cleaner look.