Normally, when a code or an animation is listing for value changes of a tag, it is not guaranteed that all values that the tag assumes are viewed by those listener.

When a tag changes its value (to 1, for example) an event is posted to all listener, but the tag value could change its value again (and becomes 2, for example) before the 1 value was seen by the listeners.

A mailbox tag is guaranteed that lets all the listener to view (and process) all its values, even through clients/server communication.

The mailbox dispatch mode is useful if you need to post some values via a tag and you want the listener code(s) to view and process all posted values, even for very closely posts.