Since my area only has one zip code, it probably doesn't, but I could see in a much larger metropolitan area it might.

We only have 6,000 people here.
Would take a mail carrier a couple weeks at most to know what address was what house or apartment.
So, the other 4 digits are probably superfluous.

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.

So it actually is a four line address?? and thanks.

If it's the last line of an address. The scanners and readers will easily determine it's the zip. A picture is taken of almost every piece of letter mail, and if the automated machines can't read it, the image is forwarded remotely to live agents working somewhere, who can provide more assistance. They would then input the needed info while the letter is still in the loop of the machine processing, and the next time it is scanned, that input would be applied to the barcode sprayed on the right lower portion of the envelope. The technology has come a long way. Of course the Post Office has a myriad of other issues that may affect deliver time, outside of an address, LOL.

Zip Codes are designed to narrow down to the nearest post office the mail is to be delivered in. The Plus-4 codes allows the local post office to narrow the delivery even more.

An analogy to Zip Codes would be National Stock Numbers (NSNs) the federal government uses. I worked in medical supply in the AF and we used NSNs not only to identify material from drugs to dressings but it helped in easily finding them in a ware house. The first four numbers are the federal stock class, the next two numbers are a NATO identifier, the the remaining seven numbers identified the item. For example, 6505-00-116-1064 is Dextrose in Lactated Ringer's Injection. When we stored them in the warehouse, we'd put them in numerical sequence by federal stock class. So if we had a requisition for this item, we'd go to the section for 6505 and then look the for item using the last seven numbers. IOWs, it pinpointed were something was the same way Zip Codes narrow where the mail is to be delivered.