What is the big deal about Big-O notation in computer science?

Question

How would Big-O notation help in my day-to-day C# programming? Is it just an academic exercise?

Answer 1

Big-O tells you the complexity of an algorithm in terms of the size of its inputs. This is essential if you want to know how algorithms will scale. If you're designing a big website and you have a lot of users, the time it takes you to handle those requests is important. If you have lots of data and you want to store it in a structure, you need to know how to do that efficiently if you're going to write something that doesn't take a million years to run.

It's not that Big-O notation itself will help you. It's that if you understand Big-O notation, you understand the worst-case complexity of algorithms. Essentially, Big-O gives you a high-level sense of which algorithms are fast, which are slow, and what the tradeoffs are. I don't see how you can understand the performance implications of anything in, say, the .NET collections library if you don't understand this.

I won't go into more detail here, since this question has been asked many times, but suffice it to say that this is something you should understand. Here's a fairly highly voted previous Big-O question to get you started.