What does the option listed in the AD connector manager called "Only once when setting up a user" mean?

What does the option listed in the AD connector manager called "Only once when setting up a user" mean?

If this option is set, the respective information is taken from the Active Directory in the XPhone Server when the user first creates a new account. If you change this information later, e.g. the phone number in the XPhone Server, the change will not be changed back by the information from the Active Directory during the next connector run. 

If the option is not activated (default), the data coming from the Active Directory always applies, i.e. manual changes made to users in the XPhone Server are undone the next time the connector is run.