One of the strange features of Soviet socialism was the existence of the free labor market:
Further, it is certainly inconsistent that each person owns his own body, i.e., his human capital, and decides which talents to develop and where to work, and the government owns all extensions of the human body. The division is arbitrary and sure to interfere with the government omnipotence required for a proper attempt at central planning. However, an old Soviet patriotic song informs us that the singer “does not know another such country Where a man breathes so freely,” that “Man walks as a master Over his vast Motherland,” and that “The young have everywhere an open road; The old are everywhere honored.” It would scarcely have been possible to sing such verses, if the Soviet economy had not had a labor market, i.e., with a fully enslaved populace. (SAtK, I, 48)
Imagine a capitalist firm. In it, the CEO can tell an employee: we want to move you to another department and pay you this much more. The worker has to comply or quit. Under socialism, he would not be able to quit. Hence, the state would assign to people their jobs.
A properly constructed socialist system would probably abolish the family, outlaw sex, impregnate women according to the needs of the central planner, take children away from their mothers shortly after birth who would then be brought up without knowing their parents, and their occupations would be determined by economic expediency as decided by the planner.
The fact that the USSR aspired to be a "worker's paradise" prevented its worst features from being implemented, by that very fact making it, instead of a full-blown socialism, a mixed economy.