Usually you think of nondeterminism as adding complexity to a system -- concurrency, randomness, etc.
So it's kind of surprising to notice that translating a deterministic system into a non-deterministic system is often the first step people take when proving things about complicated algorithms.
Planning, optimization and reinforcement learning are the canonical examples where the reason for this step is easiest to see. These are usually very complex algorithms. You could prove things about an actual implementation, line of code by line of code, but that would be a toooon of work.
If instead you can find over-approximation `inv : State x Action -> List[State]`, and if you know that this invariant is strong enough to imply whatever other properties you want, then you just need to make sure that `inv` over-approximates the actual behavior of the underlying system (either by interrogation or by construction).
It's a very simple observation, motivated by the pragmatics of engineering proofs about complicated systems, which can have a direct impact on how you think about designing those same systems. Now that huge inscrutable models are all the rage, it's a fun little FM trick I used almost every day even though I rarely work on systems that I'd bother to formally model or verify.