There is more dependence on location. I can park Brompton in an African street and nobody knows what sort of a bike it is. If a guard is in front of the store, I do not lock the bike. If someone stole the bike, they could not tell it from a no-name folder, and folders generally are of little public interest. In farther out suburban France or the US, you can lock the Brompton with a minor lock and go shopping - nobody cares or knows about any value your bike might represent. In Japan, you can lock your bike and go around your stuff because people do not steal. In Paris, France, I would not dare to blink while facing my bike from 1m away, attached to a rack with some top-of-the-line Abus. The chances of the bike disappearing during the blink are too high.
Is it really that bad in Paris. You need 3 litelok 1s. Then you can go shopping for 20 minutes. It would take any Parisiian scum with an angle grinder over 20 minutes to get all 3 of them off. A friend of mine put 3 of them on his ceravelo. Came back 15 minutes later to find some toerag working on the first one with an angle grinder. And told him the police are on the way. He ran like a scared rat.