yes, no, maybe, probably not.
That accurate enough for you?
Didn't think so. The truth is, for most people, defraging linux is a non-issue. Linux filesystems are based on commercial mainframe unix filesystems (that's a sick generalization, but it gets the point across), where having extra space between files or having a file spread all over the drive is the same as burning money. As a result, Linux filesystems are pretty good at sorting themselves out without any external help.
There are situations where defraging can have benefits, but for 95% of Linux users, defraging is a waste. That time would be better spent learning more about Linux. In fact, for many windows machines (considering that running defrag takes HOURS---because defrag wants to start over any time you move the mouse) that defrag time would be better spent learning more about Linux as well.