It depends. There is some implicit "bloat" because setting up 100 layers and accessing files through them isn't free (but caching works quite well). However the biggest problem with layers is that you can never delete data. So doing something like `RUN apt-get install foo` `RUN foo generate-things` `RUN apt-get uninstall foo` will effectively still have `foo` in the image.

It definitely depends on the use case. In many cases `RUN foo`, `RUN bar`, `RUN baz` is fine. But if you are every creating temporary data in an image the layer system will keep that around. This is why you often see things like `RUN apt-get update && apt-get install foo && rm -r /var/lib/apt`. You squeeze it into a single layer so that the deletion of the temp files actually avoids image bloat.