Since discovering "Synchronize It!" only a couple weeks ago, I find myself often using it just to compare two directories that are supposed to be in sync already (say, by SMS or another server-controlled process). I know that I can choose any action and just hit the "Preview" button, without going through with the actual sync afterwards... but I'd really feel much more comfortable about the whole thing if one of the actions listed was only a "Verify/Compare" action. At the "Preview" screen, then there'd be no button for me to accidentally hit and update the destination. Does that make sense?
(I assume many people might not want this kinda feature, so maybe it could be switched off in the Preferences for the less paranoid...)