When you pay the full cost -- that is, the full value of the resources in alternative uses -- you tend to economize. When you pay less than that, you tend to waste.
Whether someone goes to college at all, what kind of college, and whether they remain on campus to do postgraduate work, are all questions about how much of the resources that other people want are to be taken away and used by those on whom we have arbitrarily focused in human interest stories.
This is not just a question about robbing Peter to pay Paul. The whole society's standard of living is lower when resources are shifted from higher valued uses to lower valued uses and wasted by those who are subsidized or otherwise allowed to pay less.
The fact that the Soviet economic system allowed industries to use resources wastefully meant that the price was paid not in money but in a far lower standard of living for the Soviet people than the available technology and resources were capable of producing.
The Soviet Union was one of the world's most richly endowed nations in natural resources -- if not the most richly endowed. Yet many of its people lived almost as if they were in the Third World.
How many people would go to college if they had to pay the real cost of all the resources taken from other parts of the economy? Probably a lot fewer people.
Moreover, when paying their own money, there would probably not be nearly as many people parting with hard cash to study feel-good subjects with rap sessions instead of serious study.
There would probably be fewer people lingering on campus for the social scene or as a refuge from adult responsibilities in the real world.