What is Change primary DNS suffix domain membership changes

Hello,
When I add a computer to a domain I get a box that says"DNS suffix and NetBIOS computer name "
and inside it has an empty box for "primary DNS suffix of this computer"
and underneath is a checked box next to
"Change primary DNS suffix when domain membership changes"


What does this mean, and what is the difference if it is checked or not?

Thanks in advance

Here's an explanaition
http://www.microsoft.com/technet/prodte ... x?mfr=true

However, with an XP machine on a Windows 2000 or 2003 domain, you can just leave them at the defaults, ie as they are shown in your screen shot. Once you've joined the domain, the DNS Suffix will automatically default to the domain you've joined, in your case test.net and the NETBIOS name will be the same as your computer name pro10

NETBIOS is really only used with legacy (Pre NT) machines such as Windows 98.

Thank you very much for the info.