If you don't secure your SSH server, you run a decent risk of one of these script kiddies breaking into your machine. They can have their programs running day and night trying to break your machine with almost no cost to them, so you can see how the chance of it happening to you rises. Why would they be doing this? Well, say I'm one of those script kiddies, if I can hack 100, 1,000 or maybe 10,000 computers and put some script on them that just waits for the message to start connecting to some server over and over again. Well, I can turn around and sell this list of computers and the information about how to control them to the REAL bad guys for a lot of money. The REAL bad guys then turn around and use these zombie machines to denial of service attacks on some poor victim's server. Now, do you really want to be a part of that? Especially not if the server they are attacking is yours.