It's sometimes called a "cafe lock". Meaning it's generally considered an ok lock to have while you are sitting in a cafe with your bike leaning against the wall next to you.

It really depends on your area. Some areas, certain urban areas for example, call for a beefy U-lock, plus a hardened steel chain, and even then you worry about components like your saddle being lifted. In other areas, even a thin cable lock might be fine if you are just running into a store for a few minutes.