Higher gain Screen, is it worth it?

[vonzar]

What benefits come from getting a higher gain screen. I was looking at the grey wolf II 120" fixed frame 1.8 gain screen. Is this a good screen? I am getting the panasonic ae2000u and I went to projector central and did the projection calculator, and it said that with a 1.0 gain screen I could place my projector 15 feet away from the screen, which is almost exactly where I need it. But when I change the screen gain to 1.8 a message comes up in red that says Recommended image brightness for rooms with ambient light. So does that mean that if I don't have ambient light, the screen will be a bad thing? Will I have to change the brightness on the projector to accommodate? What does a higher gain actually mean for image quality? Is there a difference? I am making my first ever screen upgrade since my brother gave me his and my first projector upgrade since I bought my in72 (my first projector) at the same time, so I don't have much experience in this field. Any help would be appreciated as I will be purchasing the screen and projector in the morning. Thanks