Isn't he saying that you should always use a container?

Any content should always be in a container. The 15px margin keeps the content from laying against the side of the browser. If you want to do a fullscreen background or image or something then you don't need the container.

Exactly this. If you want to create a bleed, don't use a container, but if you want content inside that bleeding element, put a container inside of it, which will keep content from bleeding.

If you need multiple bleeds on a page, use multiple containers. Just don't nest containers inside of containers.

For bleeds I just use the same container structure inside of a wrapper div that has the bleed.

For images that you want to touch the side or whatever, there is some of that fiddling with the margins on the interior elements, yeah.

.col needs to be in a .row which provides clearfix, of course this is only one of the reasons.