Well, in RL, any gun shooting at you is a threat to your life. However, in AH, the BB gun does almost nothing except annoying the other guy and maybe make him duck a bit. (But of course, there are always lucky shots). The saved weight would increase climb rate, turn rate, and speed, even if it is just a little bit. Kinda like the same of why people choose to fly without gunpods. More guns is good right? But saved weight and drag is even better.