With anti-theft software installed on a Macbook, is having a login password a good thing?

My friend has just been burgled and lost his Macbook. He didn't have any anti-theft installed - but this made me think that I really should get some.

I've found various options, including Prey.

Here's the thing, though. I have a system password on my Mac that I require every time it resumes from sleep.

If it gets stolen, the thief will get it home, and open it up. But they'll be stuck at the login screen. I'll have told Prey that it's missing, but unless the thief can connect to Wifi the Mac will never be able to connect to Prey to send me its location and/or pics of the perpetrator.

Does that mean that, for Macs (or generally, for laptops without 3G connections) anti-theft software may actually work better without requiring a system password when opening the computer?