Czech person here, my friend studied Communist economy at the Economic University of Prague (VŠE), did his master thesis on the subject, and I asked him this particular question to get a 20-minute lecture.

The core of the lecture: centrally planned economy of Communist Czechoslovakia tended to err on both sides. There was a shortage of some goods and surplus of others. Advertisements were meant to drive up demand for the excessive goods, thus emptying the warehouses.

One notable difference to free market ad culture was that brands and trademarks were almost never cultivated in Communist advertisements. They were much more generic. An abundance of milk? "Buy and drink milk, it makes your children healthy." No brand to be seen.