So, there is a direct effect of this that's really annoying when you bump into it. Docker images are tarballs, and the layer cache relies on how the tar file is constructed. The same layer content constructed by two different tar implementations will appear different to the cache lookup.

For reasons known only to themselves, Docker originally used different implementations for the docker command-line tool and the docker-compose tool. This means that cache entries produced by two tools that you got from the same place don't match up, and you can't use one tool to cache a layer and have the other pick it up.

At least, not by default - if you know about it, there's a switch you can flip to have one use the other's implementation. But they had to add that in, and do that extra work, because tar isn't well-specified.