Some people are happy to wait for the progress bar in a setup screen to tick to 100%.
Power users would rather create a script that'll do it for them, without locking up VMware (still leaves the disk locked, but you can still run other guest machines).
To run a defrag from CLI:
"%PROGRAMFILES%\VMware\VMware Workstation\vmware-vdiskmanager" -d "X:\Virtual Machines\Windows 7 x64\Windows 7 x64.vmdk"
To defrag ALL of them in one line:
for /R .\ %i in (*.vmdk) do "%PROGRAMFILES%\VMware\VMware Workstation\vmware-vdiskmanager" -d "%i"
This scans recursively for any vmdk files and runs the vmware-vdiskmanager command on it.