A comment Eve just made on a call prompted this
Consider some magazine at which I've subscribed. The mag only needs my address at the start of every month, just in time for sending out that month's edition.
Their demand curve (I'm sure there is a proper economics term) for my address looks like
If the magazine relies on me actually visiting their site (to view online content etc) as the mechanism by which it can get the most recent address, then they are at the mercy of my erratic visit schedule for the update operation.
If I happen to move in mid February
then I don't get the March edition.