You may have to choose one FS over another, and you will want to make such a choice intelligently.
Persistence is a key idea here.
Unlike most other data structures that an OS manipulates, the FS and its contents survive intact across system reboots. A file has a name which enables a user to manipulate it conveniently. Talk briefly about sequential vs random access. Traverse through and process all the files in the directory, given some operation to be performed on each file. From a user's point of view, these design decisions will not be highly visible.