mail in ballot

Big Day for Lockwood
Today is the day when your ballots have to be postmarked or received at the courthouse. For the folks in Lockwood, you will decide on a new high school. It's a big issue with a big price; so, either way make sure your voice is heard.
Do Not Delay
While sending in my mail-in ballot, I noticed a message on the front to the post office that says "Official ballot. Do Not Delay." It made me wonder why we need that; is there mail that they do delay? If so, why?
If two pieces require one stamp why does one get better delivery than …