Well,
as explained, some people will need a next-day service. Some people aren't in that much of a hurry.

A lot of post goes through Royal Mail. If they separate it into "urgent" and "not that urgent", they can prioritise.

Rather than assuming everything is urgent, they can divert all the stuff that isn't all that important, put it on a slower track, it'll get delivered when it gets delivered. If the truck/van/bag is full, the second-class stuff can wait for the next outing.

A lot of stuff is sent second-class, particularly business post, spam, etc, so this does help free up more people to make sure first-class stuff is delivered on time.

I think it's all based on prioritisation, anyway.
( Thinker, Fri 4 Jul 2008, 14:56, Reply)