Gas Fireplace: Is mesh screen panel in front of the glass necessary?
Without seeing a picture, I'm going to assume you're talking about the "safety screen" that now comes with most fireplaces.

It's necessary for manufactures to provide them, but whether you put it on or not is up to you. The intent of it is to stop small children from burning their skin on it if they get too close to the unit, but if there are no children in the house then it serves no point.