When filing systems fill storage address spaces past a certain point, system performance can become unacceptably slow. Also, the presence of old, unused data adds time to time-critical processes like backup, virus scanning, and system management practices. Capacity management is the process of relocating files from primary storage and placing them on second tier storage where they do not interfere with production operations.
One of the questions that eventually comes up is “Should capacity management be called storage management or data management?” Although it is often referred to as storage management, it is actually a filing-level process. The point is to return empty blocks to the file system's free space pool.