I think that having house numbers is very important. If you don't have a number on your house than perhaps the street marker will do.
It makes it so much nicer when you move into a new home and have to have things delivered or people come visit.
You must have them in order for the home to be found. The other important factor is if there is an emergency. I live in a rural area and without the marker they could waste time finding my home.
Quick response is important if you are hurt or the home is on fire. You don't want to wait a second longer than necessary.