The host name value is very handy if you have several servers and want to use the same domain for all of them.
You can reach them by giving each server a unique host name.
e.g. "alpha" for the first server and "beta" for the second
the domain value can be any domain you own
My DNS has two A entries for getting to ISPConfig control panel
alpha.myhosting.tld A 119.68.xxx.xxx
beta.myhosting.tld A 88.43.xxx.xxx
Of course you can also reach the control panel by using the IP as the name.