CatBus said:

Wasn't there a thread about Vader's floating glass of water in the original drafts for Star Wars, which made it into a comic adaptation? Basically the guy can't even be bothered to hold his own cup--it's the very definition of frivolous use of the Force.

We'll never know exactly why that wasn't filmed, but I like to think part of it was that in the early days, Lucas accepted criticism and when people told him something was idiotic and unnecessary, he didn't do it.

The fact that he wears an all-concealing helmet probably played a part in the decision as well. ;-)