I don't remember where that big discussion would be.
Biggest problem with reinstall in the form of uninstall+install would be that you basically reset some components to their factory defaults: any customizations by the user are gone. For example, an add-on sets the mailhost to localhost, an administrator customizes it to example.org, and on reinstall of the add-on it may be reset to localhost again.
This used to be a big problem with add-ons that relied on five.intid: reinstalling five.intid or plone.app.relations would throw all existing intids away. That particular problem has apparently been solved in 2009 already, but similar problems could occur if you are not careful.