Communists believed that their system would be much more efficient than capitalism: They thought that competition between companies was wasteful.
Why build three separate headquarters for carmakers (General Motors, Chrysler, and Ford), when you can just build one?
Why have three advertising budgets? Why pay for three CEOs? Why not put all the factories together, so that the same engineers can fix problems at all of the plants? Doesn't one large firm maximize economies of scale?
These are all good questions. So why do you think Communism turned out to be such an economic disaster, when it sounded like it would be so efficient?