I rarely, if ever, use a lock on a folder.
I once locked up four folders and a MBT in York to catch a boat. They were all locked to a steel post and intertwined with each other than it would have took a long time to extract any one of them. I was only gone 1/2 hour. No problems. Although I realised that they I had not really connected to the post when I returned.

Other than that I sometimes lock a folder at bike shows as any thief would stick out a mile.

As a rule I never lock up a non standard bike that would be difficult to replace on insurance. Ie my black upgraded Mezzo. I always take my bike indoors at work.