One problem with a lock & chain is that any bozo with a throwaway masterlock can put it on your chain, and then you're stuck. You can't unlock your own bike. Also, this person could probably argue with a police officer to cut off your lock claiming that some bozo put their lock on his chain. I had someone put a lock on a chain of mine once, but they didn't close the lock completely. I don't know if they were giving me a warning or what, but I don't use a lock & chain anymore.