It's not perfect. I wonder how it is tied to the service? Serial Number would be funny. Sell your Mac and constantly annoy the buyer by locking it.
Joking aside, if it's software based, it is still better than nothing. A tech-savvy thief may know to disable Airport immediately, but at least it is still one small extra chance of recovery.
I think it's more to do with data protection than recovering a stolen laptop.