Suppose the only thing you know is that your algorithm runs in `O(n^2)` time in the worst case. From this very fact you know that the upper bound looks like `Cn^2` for some `C > 0`. Thus you know how the upper bound of your algorithm scales, namely, if you double the input size the upper bound quadruples.

***Question***: What practical question can you answer if you know the way the upper bound scales? I just can't understand if this particular knowledge is helpful in some way.