The plus four changes all the time so it isn't feasable to know it. The use is large mailers can get a discount by looking it up and presorting mail. If the mail coming into my post office has my mail next to my next door neighbors that saves them a lot of time.
>>bluGil+(OP)
Is that still true? I would imagine any reasonably modern computer could map every physical address in a huge region to a (route number, stop number) pair. I wouldn't think the +4 would add a lot of value anymore.
>>kstrau+Ha
The sort everything outgoing by where it goes on the truck is valuable. sure computers can sort but this is physical things and so mechanical limits apply.