This site has helped me feel more confident--even assertive--about taking my folder indoors in a variety of circumstances. That, of course, is a major (but not only) benefit of a folder. However, in the short time I've owned one, a lock and chain has been a deal-breaker several times: either because of cramped and crowded spaces or not wanting to bother with interactions of a doorman or coat checker. I'm also familiar with many college campuses. Owning a lock and chain doesn't mean it has to be used all the time, but when thinking about the OP's question, I can imagine many instances when carrying the extra weight would be preferable to squeezing into some college environments with a Brompton, small as it is.