FAQ General information - What is "disk optimization"?
Imagine a big library with lot's of books, spread out all over the
building and not sorted whatsoever. There is an index telling you exactly where
every book is, but you will have to walk a lot when you need
several books. This is exactly what happens on your harddisk,
the files that belong to an application can be all over the place, anywhere
on the harddisk. Optimization will bring all the files together in one place,
leaving the rest of the harddisk empty, and will sort the files, for example
alphabetically.
See also:
What is "disk fragmentation"? Frequently Asked Questions