1. Grass uses a lot of water and maintenance. A lot of ground cover need less water and maintenance.
2. Some area are just too shady for grass.
3. Many of the ground cover do not need to be mowed.

The downside is that your local HOA or municipality may make you have grass :-)

Paul

hmmm thanks for the information. I never thought it this way :)

This might be helpful if you are in Florida.

http://www.floridayards.org/index.php

Basic theory is grass takes up a lot of water where you can put native plants and mulch in that does not.

I have a couple strips of grass that are useless for recreation that I'm going to turn into native plants with mulch.