There are times that you may want to have different access to different areas. an example for home use that I have come across is with an outside garage. A customer has a garage that he works on cars and projects for various people, and he has a couple people that help him out. I was able to set him up with key 1 for the house key 2 for the home and key 3 for him which opens both house and garage so he does not have to carry more than one key for both areas. Small business owners find it quite useful. another area it can be used is a building that has an office that the managers only want employee access to the main area but not the office. the managers have one key for both doors but there are separate keys for the building and office. this system can grow to hundreds of levels for large commercial areas as well.