The Change Threshold Specifies the percentage of user records that can be synchronized from the LDAP User Store to the VIP Service. This applies to the update, delete, and the add operations independently. The percentage represents the number of user records that can be synchronized from the LDAP User Store to the VIP Service at anyone time. The synchronize option only deals with the users in the user store based on the selection criteria you selected. The % should be based on the amount of users you have, as a large user base will take time to sync if its set to 100%. This applies to the update, delete, and the add operations independently. Selecting the run once option does the sync at 100%.
So to clarify, if a company has 500 users based on Userstore criteria and 20 new users are added to the LDAP database that match the user filter in the User store, only two of them will be synchronized based on the threshold of 10%. The update, add, and delete operations would each do 10% independently. In this case the two users would fall under the 10% for the add function. In addition, you cannot specify any threshold for synchronizing administrator records.