Originally posted by: Shadowknight
As they pointed in Babylon 5, one of the advantages of PPGs (sort of their version of an energy weapon) is that while powerful enough to kill someone, unlike a bullet, it doesn't have a chance of hitting a window or a weak section of the wall and rupturing the hull/breaking the window. Obviously, a bad, bad idea in space. Bullets also can ricochet off hard surfaces. With a gun, you have to reload when you get low and have to make sure the ship's stores are reguarly restocked at space stations or planet. With energy weapons, you just recharge them from the ships electrical system (powered by a nuclear reactor/antimatter/whatever a sci-fi ship uses for energy). With an energy weapon, you can usually just use it until the battery runs dry, depending on how much of a charge it holds. If you need to carry a large supply of "ammo" with you, having a few small batteries will weigh less vs. a crapload of bulets.
Plus, y'know, energy guns look prettier in design that guns. With the exception of the colonial assault rifles from Aliens.