True, but studying the theory gives a better intuition for big-O. And theory is helpful for some of the edge cases that can be more complicated. For instance, I wouldn't want to try to determine the run-time of a recursive algorithm with just the info in that article.
Indeed, and if you did learn these things through experience, as I supposed, then you probably did so by writing something O(2^n) and suffering when you had to process >100,000 records.
(Why does it take 100 ms for 10,000 records and 50 minutes for 100,000? ... hmm)
Learning these concepts through the theory is definitely more efficient.
If you have a lot of experience, you probably already understand the concepts. The notation just gives a clear way to describe them: https://rob-bell.net/2009/06/a-beginners-guide-to-big-o-nota...,