It creates the possibility of companies, which are selling a certain product on a market which does not have any other producer, becoming and having the 100% of the market share.
This enables them to completely determine the price that can be very high as people will have to pay if they want to have this product.
It also enables them to determine various aspects about the quality of the product in general.
Usualy all this would be determined by the demand and competition. But in a command economy, all of it is determined by the producer. All the products can therefore look the same and don't need to be produced in excess but in just the right amount for the people which is obviously very hard to determine.
