Locks of almost every kind merely provide the illusion of security, but the majority of time that is enough. They act as visual deterrents to less determined thieves, but if someone is bound and determined to get what you have, there is very little you can do to stop them. Slow them down maybe, but not stop completely. But most thieves are only interested in quick, easy scores, so even a cable lock will serve it's purpose in this regard.

I watched a video once that a thief made to demonstrate how easily he could break into a number of cars and steal their belongings. It was a smash and grab job, but he was in a parking lot at night and he literally just moved from one car to the next, smashed the driver's side window, picked up the valuables that were in plain site, and moved on to the next car, and I think over a couple minutes he managed to break into something like 10-15 cars, seemingly without a care in the world. His speed and efficacy and sheer ballsiness was shocking. Dude gave absolutely no fucks. Not sure what his haul was, but he had a bag full of goods when he was finished. No idea if he ever got caught.

I agree that it's important that someone have a particular goal in mind when attempting to secure something like a bike. You're either looking for a visual deterrent, something to slow a potential thief down, or something with as close to real security as you can get.