What effects does the lack of competition in command economics have?

When your market share in a certain area of economics is big enough, you can start doing things you usually would not do. As you basically determine various buying factors of the goods (value, size, quality ...) that are being sold (as you do not have much competition which could remove you). Due to this, in command economics, all the products can look the same and the amount of goods that are produced can come short to the actual demand; the demand being bigger than the amount of goods that are produced.