Security is a deterrent, not a guarantee. Recently I had my saddle stolen (along with seat post), and a simple clamp style seat collar would have probably prevented it.

Depending on your area you may need a few different types of security devices. You can use a Pitlock for your wheels and seat post. A leash for your saddle. Then a U lock for your bike frame.

Basically you are trying to prevent opportunity based thefts and deter "professionals (soulless scum)" to go for easier targets.