It's hard to believe that the only reason we have some of these iconic creatures and robots is because an actor was willing to be stuck inside the costume for hours. Those costumes are not comfortable. Imagine if I shoved you in a trash can and made you roll around making beeping noises? You probably couldn't pull it off. I mean that you couldn't pull the trash can off. You're too fat. OOOH! Burn! But really, it would be hard to act while inside some of these costumes, so major props needs to be given, even if all the acting you're doing is rolling around.
Thank god for the little people. They definitely need to give more roles to little people, but their stature has made for some iconic roles, like the munchkins in Wizard of Oz, or any short robot/creature in Star Wars.