A good example of this is for the the format one wishes to send messages in.
That one in particular I wish was also in the formatting toolbar above the message composition box, as an ad hoc override to the default one sets in one's account preferences.
On that page the preference in relation to this is listed as "Post Preference," which I also think is not precisely clear as far as e-mail participants are concerned.
It has no effect on email posting. It is only for the on-site composition pages (including Wiki as well as messages).
