Disabling external images was the default until they started proxying+caching the images themselves. So now _by default_ clients get to see the images without sending tracking data to the senders - Google doesn't like competition.
I still keep the images disabled, though. In most cases, you don't care about what's there in the images anyway.
I still keep the images disabled, though. In most cases, you don't care about what's there in the images anyway.