The DU Lounge

that it definitely could.
Mail carriers get trays of mail sorted by machine called "DPS".
These trays of mail are given to them ready for them to take out and require no additional sorting.
The plus four of a zip when read by sorting machines, allow the mail to be sorted to not only a zip area, but to a specific street or even apartment building.
But sorting machines are getting so much better and quicker these days that on a clearly legibly addressed piece of mail, they can often accomplish the same detailed sorting, even without the plus four.