Can someone please explain what the "Container" layout element would be used for, please. I understand the sub grid but not the container. Thank you.

I don't use RLM (yet) but in the quick start guide it does explain a little. Check out this page here, and start with the second paragraph . . .
http://www.coffeecup.com/help/articles/managing-the-responsive-grid-with-layout-maker/

I take it as an element with no styling presets.

I think of it like this:

In my design I want a Green box inside of a red box inside of a yellow box. How do I accomplish this in RLM?

Easy...

I set my Column to Yellow, I set my subcoloumn to red and I set my container to green. Which gives me my desired effect.

Now, it is not only used for that. In the Pulsar theme it was used to add additional padding and margins for the services boxes and icons that are used at the top of that theme. Making them more appealing and easier to work with.

You can use it on any element you need it for, just remember it adds more code to your layout. Thus, should only be used when needed.

Thank you guys, appreciate the answers