Before installing WUBI, should I defragment the disk?

Wubi is an Ubuntu installer for Windows that lets you install and uninstall Ubuntu from a Windows desktop. Wubi adds an entry to the Windows boot menu which allows you to run Linux. Ubuntu is installed within a file in the Windows file system (a loopmounted partition), this file is seen by Ubuntu as a real hard disk. That way the hard drive does not have to be repartitioned before the Ubuntu installation. The resulting Ubuntu installation is a "real" Linux system, not just a virtual machine. Wubi makes it easy for Linux newbies to play around with Ubuntu.

But if you have less than 5 GB space then you can defragment disk for more space optimization ..increase access speed by rearranging files stored on a disk to occupy contiguous storage locations

this is my personal opinion