The idea behind both InstallEase and Composer is simple: suppose you want to install a new application on 20 computers, complete with plugins and pref files. Rather than walking around to each one, you snapshot your pre-install state on a prototype machine using InstallEase, then install the software; finally, take an 'after' picture. Just like that, you've created a package installer that can be run by the individual users, pushed out with ARD, LANrev, Casper etc., or triggered to run from a remote server. It's a great timesaver, especially for programs that don't leverage Apple's .pkg installer format for standardized deployment -- Office 2004, for example.
If you've got a passel of Macs to manage and you haven't tried InstallEase yet, give it a download and check it out.