In big cities (USA and Europe) it is really nice to have a good U-lock (like Bulldog) and a cable, even though they are heavier than all h*ll. When you want to go to a museum, you have to lock up securely. Now, I am told that some people use hotels instead of camping all the time. In that case, you could enjoy the security of putting your bike in locked storage. One good trick (for campers) is to lock your gear up in a train station locker (Europe only, as lockers no longer exist in the USA). On the other hand, when away from big cities I have often carried only a small locking cable to keep a thief from just grabbing my bike, and that has been sufficient.