The importance of each of these variables depends greatly on how the product will be used, the type of data being compressed and similar factors. The compression time is the total amount of time it takes a user to compress a set of files or folders. This should include the time to launch the compression tool, select the files to compress, create and name the compressed file, perform the compression operation, close the compressed file, and exit the application. Some applications provide a variety of ways for a user to compress a file, speeding up the process tremendously.
Some examples are drop boxes, contextual menus, compression via renaming and the like.
Additionally, some products can be scripted to run automatically or run at night. In these cases, the compression time can be discounted as if it didn't exist, since the user isn't there. This gives the amount of the file that was removed. Compressing already compressed files is unproductive and unnecessary. Compressing a file that is smaller than a single disk allocation block, regardless of how much compression you get, will not save any disk space, i.e. a one byte file takes up one disk block and a 100 byte file takes up one disk block.