Bike locks are a spectrum, and I've generally sat on the small and light end of that. My reasoning is that any lock can be broken, it's more about how difficult you want to make it for the thief.

I'm happy with any lock that prevents someone from just picking up the bike and riding off. As soon as someone has to bring out speciality tools, they're breaking the social contract regardless of those tools being hydraulic jaws and angle grinders, or just bolt cutters. That's the step in trying to prevent.

So I just roll with a thin cable and a little padlock. Small enough to chuck in a pocket, long enough to wrap around fences/trees/friends bikes.

Your mileage will definitely vary.