Okay, why do you use a hash table instead of a linked list when quick retrieval is more important than in-order traversals?
Now, it's pretty obvious when we're discussing something as simple as this, but this is the fundamental essence of Big O. Certainly, we don't need to calculate it on a daily basis, especially past the general case, but it also doesn't hurt to have common terminology when speaking about an edge case of an algorithm.
And just having a general feel of a graph of how quickly an O(n^2) algorithm can spiral out of control versus an O(log n) algorithm is useful. (That is, if you have a small amount of elements, it's not going to matter, but it will matter quickly as the number of elements grow.)
Now, it's pretty obvious when we're discussing something as simple as this, but this is the fundamental essence of Big O. Certainly, we don't need to calculate it on a daily basis, especially past the general case, but it also doesn't hurt to have common terminology when speaking about an edge case of an algorithm.
And just having a general feel of a graph of how quickly an O(n^2) algorithm can spiral out of control versus an O(log n) algorithm is useful. (That is, if you have a small amount of elements, it's not going to matter, but it will matter quickly as the number of elements grow.)