It's certainly useful when you find that someone accidentally made something n^5 instead of n and you need to explain to that person why they were very, very wrong.
Yes, this discussion happens with junior engineers. I keep finding O(n^2) code that should have been O(n) or O(n log n), and not just as an academic exercise, because it slows the website down.
You don't code the notation. Knowing how to write optimized code != knowing the notation. I have hardly seen the notation outside interviews.