Defragmentation alone just recombines any files that are broken up into more than one fragment. Having the files themselves contiguous gives the quickest enhancement to performance, removing the need for multiple head seeks to read from multiple fragments. This takes no notice of where the files are located on the drive, simply that they're each in one piece.
Optimization re-positions any of the files that would benefit from being in a different location, judged by a few criteria, such as boot optimization (placing the boot files in order required at the start of the drive) or compaction (clustering files as close as possible to the FAT or MFT).
This is time consuming, and re-positioning of files is required less frequently than simple file defragmentation.
I believe drive optimization would be needed much less than weekly, especially as Windows since XP has done background defragmentation, including boot optimization after every third restart cycle.
Edited by Platypus, 30 November 2017 - 08:49 AM.