Note that the SilentAgreement is work-efficient, but it is not time-efficient for the author (see also SilentWelcome). The author has to go slow and listen, wait for reactions. Positive feedback (a warm reaction) will show the author that he is on the right track and allow him to move on faster and with more confidence.
Note that one can only assume SilentAgreement of those contributors that are active on RecentChanges and of the members that can be expected to check rc at least every other day. If you are in a foreign wiki that shows no activity, the assumption is invalid.
To go for SilentAgreement makes sense if there is no reason to hurry and if the risk of (discussion + undo) seems large compared to the nuisance of (suggest + wait). See also: AgreementMode.
Contrast [Warnock's Dilemma], which suggests that a lack of a response to a posting provides no definitive information.
WikiPedia specifically dissuades the usage of SilentAgreement to pass policy, requiring actual AgreementModes (calling 'em StrawPoll?s). Then again, they have a lot of policy, and a bit of bureaucracy, being in the way of establishing more policy, is essential to not being too top-heavy for work to take place... not that I've ever tried, but I hear passing policies over there is nigh impossible! -- NatalieBrown