Expedite items have a high and immediate cost of delay. They should be started at once and given priority over other items. Fixed date items have a high cost of delay once a threshold is passed. They should be started before there is a significant risk this date will not be met. Standard items' cost of delay follows a fairly shallow S-curve, in other words, there is no reason to expedite them - they should be handled normally. Intangible items apparently have no immediate cost of delay, though it is expected to rise at some more distant point in the future. Such items are useful background tasks to be handled when there are no more urgent tasks.
At a recent Kanban Masterclass I attended, David introduced an example to demonstrate the difference between Fixed Date Items and Standard Items:
A hotel/resort site wishes to offer two special promotions: one for the Spring/Easter holiday; one for Valentine's Day. Because people tend to book much later for Valentine's Day, the opportunity-cost of delay is likely to be much "steeper" - more like the Fixed Date case, compared to a more "Standard" shape for the other promotion.
This led to consideration of what the revenue projections for different release dates might be in these 2 cases, so I undertook to produce some sample data for discussion. Here they are.
Taking all the potential release dates and plotting the opportunity-cost for each delay produces the graph above - an S-curve showing little impact initially, rising more rapidly after the first couple of weeks.
Let's compare that with the simulated data for the Valentine's promotion.
In this case we are expecting nearly all the sales to be made in the last couple of weeks before the event. It really doesn't help to launch early because people won't book early any way!