[ncmncm]

There are only two important things taught in CS that most people don't seem to pick up on the job. The most important is order notation. The second is the relation between grammars and state machines. Both are worth as much attention as you can afford for a week.

Things not taught in CS that you need to know on the job are legion. By far the most important of these is the use of invariants. Second might be the memory hierarchy, and cache semantics. Third might be use of bitmaps and bitwise operations.

[iudqnolq]

I'm learning about invariants in a relatively introductory cs course and I've been told they end up being relatively useless in actual practice. When have you found them useful?

[ncmncm]

Invariants are essential when designing a system, to ensure the resulting system can be understood by actual humans who will be responsible to maintain it.

They are right that invariants will not be essential for your assignments, at least for the first couple of years, although they would save you from some dead ends.

You will be able to code some of your invariants as assertions, but as often not. The ones you can't are the ones you have to pay the most attention to.

If the system invariants get too complicated, or hard to express, the design is wrong--reliably. That is when they are most valuable. Millions of systems designed without invariants could have been right, but we're stuck with what we got, instead.