It's worth noting, as others have done, that cable locks are extremely easy to cut. It's much easier than other things. I cut one with a cable cutter, the kind used for cutting brake and gear cables on bikes. I had to make two or three snips, but it was quick and easy, rather like using scissors.

Use a lock that is appropriate for the environment. I used a cable in the NJ suburbs. No one stole my bike when locked that way. However, I would expect it to get stolen if I locked it that way every day at a suburban train station.