It does make sense. I just don't claim it makes total sense. Nor do I ever tell any other poster their post "doesn't make sense"...it's rude. Perhaps you don't care.
Here's an example: From the command line, you type 'service network restart'. If you only had an entry in rc.local, the second (alias) IP is now gone. If you follow the howto, it's still there.
I don't know if any server-manager panels ever restart the networking, but if any of them do...
G
p.s. I'm not familiar with the 'ipaddress add' command you specify, nor do I find it on a SME test box I have on hand.