It is used for setting the reconciliation options for the email accounts. For each mail account you can state whether you want the e-mail deleted on just the handheld, or the mailbox and handheld; you can tell the device if you want to enable or disable the wireless reconciliation; and configured how conflicts are handled.
it is the action of your email on your phone and the actual account you have synchronizing with each other basically. instead of your mail getting pushed you force the device to pull it in that instance. in lamen's terms