Some people somehow just don't get plaque for some reason so in that case it's maybe pointless, but most people do.
Brushing twice a day, properly (with good toothpaste and a good electric toothbrush) basically eliminates the need for flossing.
EDIT: ITT, people who don't realize flossing is terribly ineffective and hasn't been recommended by the US government for a decade now, because studies showed that the floss wire doesn't provide enough friction to actually effectively clean anything. If you find that despite thorough brushing you still build up plaque, occasionally use a toothpick instead.