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. Now we have three complete idiotic and unnecessary films, so yeah, frivolous use of the Force comes right along with that.

IIRC, it's in the novel, and merely illustrates his mastery of The Force, before choking Admiral Motti of course. He summons the cup into his hand. I never thought it frivolous.

I think when it came time to shoot, they probably decided there was just was no way to make a guy in a scary mask drink from a cup, and not look silly...