Actually, having never been away from Illy more than a week or so, I have yet to draw full advantage of sitting, however, I have allowed new players to sit my account in the past so that they could send themselves basic resources from my cities, meaning I dont have to.
I know thats not how sitting is intended, but it really makes the game far more enjoyable that you can assist your allies with resources without having to go through the daily tedium of dispatching caravan after caravan. Maybe this feature could be altered to fit the game/intended purpose, like e.g. a pool of allied cities providing free resources for the new players to pick up as they like.
I have to say I disagree with Jane about the sitting option never being used at it is intended tho - many of my allies have utilised the sitting option when they have gone off for a holiday. Even if its just to allow little tweaks and details to be sorted while away, its always good to leave your account in ACTIVE hands - that way you don't get any nasty surprises when you come back.