Verify INSERT permission, Verify UPDATE permission, and Verify DELETE permission
Determines whether to check during synchronization that the Subscriber login has INSERT, UPDATE, or DELETE permissions on the published tables in the publication database. The default is False because merge replication does not require these permissions to be granted; access to the published tables is controlled through the Publication Access List (PAL). For more information about the PAL, see Secure the Publisher.

You can require permissions to be checked if you want to allow one or more Subscribers to upload some changes to published data, but not others. For example, you could add a Subscriber to the PAL, but not give the Subscriber any permissions on the tables in the publication database. You could then set Verify DELETE permissions to True: the Subscriber would be able to upload inserts and updates, but not deletes.