(Edited you reply so you new question wasn't in the quot box)
Well, if you analyze an installation, you do exactly that.
Sometimes the programs own uninstall feature leaves things behind. Meaning that if you install a program, it may put 10 files on you hard-drive, but upon uninstallation only remove 7 of them - leaving 3 useless files behind.
What the analyze feature in ZSoft Uninstaller does is that it scans you registry and the hard-drives you select for registry entries and files.
Then you install you program, and run the second scan.
Then the ZSoft Uninstaller Installation Analyzer compares the list of files and registry entries there was on you computer before you installed the program, with the list of what's on you computer after you installed it, leaving only the changed files in a new list witch it then saves.
In this list is (almost) all the changes the installation program (or whatever you've done) have done so that it can be reversed (files deleted, registry entries deleted and deleted once recreated) completely.
Hope you understand.
As always, feel free to ask questions.