How many Domain Names do you need?

In setting up MySkylla I ran into a puzzle? I had various servers hosted by different companies and each server needed a domain name, commonly referred to as a domain.
I didn’t want 4 or 5 domains due to cost and more importantly each additional domain made things increasingly complicated.
The solution was creating sub-domain names (CNAME).  Yes, you can have a domain that uses services from various hosted or dedicated servers, websites, email services, google apps & more from various companies all with just one domain name.