Nagios doesn't auto discover the services running on remote hosts. If that is all you want, then there are other apps, similiar to nagios, that do.
I've installed and used many of those, and they are junk, IMHO. None of them have a parent relationship, so therefor, if one cable becomes unplugged, you might get notified 1000 times via email about each and every host being down. But with nagios, I get one email about the "blocking host" and that is all I get.
In nagios, if you don't add a definition, then you don't make a check. Choose what is important to you, and define them to be checked. After doing one or 2, it's quite easy.
6yy yank the next 6 lines
change the hostname, ip, whatever and you have added another check. Not real hard nor time consuming.