4. Monkeys should be fed face-to-face or by telephone, not by mail, email, instant-messaging or whatever. Because if it is done in writing, the next move will be the boss’s (remember?). Documentation may add to the feeding process, but it cannot take the place of feeding.

This is to make sure that the meeting serves making decisions and moving forward - and not stuttering the process by a back-and-forth of time-consuming feedback loops. 

It also ensures that it's always clearly the responsibility of the subordinate to keep it moving, because he/she is not "waiting for the boss to answer".