Simply put, I like my privacy. I originally acquired a PO Box to have an address associated with my domain registrars. You have to have a physical address as a just in case. In this instance, I use a PO Box as otherwise, a billion people will know where I live, and I don’t want that.
With this in mind, I decided to publicize my PO Box in the case that someone would want to write me. As of when I check my box, it is usually on Mondays, and Thursdays. Since my PO Box is a 5 minute walk away, I can check it on a frequent basis. These days are also when I drop mail off that I received.