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.
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.