Prebuilt CircleCI Images Bad Practice?

Maybe I’m crazy, and I hope I am. But, I was watching this video about using prebuilt images from CircleCI.

But one of the main reasons we use Docker is that the SAME environment that I develop in, is what is tested, is what id deployed.

What is the benefit of using these CircleCI images, and do they invalidate your tests by changing the environment?

Some people don’t know how to, or don’t want to build their own custom images.