There are cases where you must adapt a known algorithm to fit your domain. In my job, for example, we work with automatic train dispatch planning [1]. The application is built in Java and one of the main components of the route planning is a custom depth-first search. The search tries to move a train through a series of connected tracks while considering the passage of time and checking for time-dependent constraints such as track blocks, other trains, speed restrictions, etc. This couldn't be done using a standard library implementation.
Also, I believe such knowledge will make you a better programmer, even if you don't have to build everything from scratch. I have seen experienced developers using a list to store unique elements, when the only read operation they would do was to check if an element was in the list. Their solution to speed up the checks was to sort the list every time it was modified and then run a binary search. In this case, better knowledge of algorithm complexity and data structures could lead to a much faster solution, using a set for example.
Also, I believe such knowledge will make you a better programmer, even if you don't have to build everything from scratch. I have seen experienced developers using a list to store unique elements, when the only read operation they would do was to check if an element was in the list. Their solution to speed up the checks was to sort the list every time it was modified and then run a binary search. In this case, better knowledge of algorithm complexity and data structures could lead to a much faster solution, using a set for example.
[1] http://www.academia.edu/6128585/A_Heuristic_Approach_to_Trai...