We all get to choose how much lock to carry. If you want to carry a 10 pound chain and lock, a 3 ounce lock, or anything in between that is fine.

Me... Even when I was carrying 45 pounds of gear I considered a lock to be somewhat optional. So far I have compromised by carrying a light lock. I used a 12 ounce lock on previous trips, but plan to go to a 5 ounce one on my next trip. In small towns I consider just about any lock that requires tools to break to be adequate. In a big city I figure no lock is really adequate. On tour I mostly avoid cities and tend to get a room or stay with a host when I do stop in a bigger city.