The template directives are removed before the page is actually sent over the network, so I don't see how it would have any effect on bandwidth, one way or another. As for the comment in the POD about "dramatic savings in bandwidth," I believe they are making a joke. The size of the POD would be dramatically smaller without using comment-style directives, thus saving huge amounts of bandwidth transmitting the documentation.

Update: for what it's worth, when I wrote my first reply, I did miss the part of your original post where you mention the comment-style directives. I apologize for that, but hopefully this post will reassure you of their use in the future.