By default cache replicates immediately after commit. The difference between ASYN and SYNC is that the former does not wait for the other members to acknowledge the replication and returns immediately.
Batching can also be enabled, with "UseReplQueue" attribute. Take a look at "Configuration References" in the user guide for details on how this works.
Apart from what has been answered earlier ..
-- if you need your changes to be replicated only after a certain number of changes happen, then use the UseReplQueue and ReplQueueMaxElements in the configuration.
-- if you need the changes to be replicated after a specified interval use the ReplQueueInterval element
Great information, thanks for the replies.