[e12e]

The "container" is common, but typically not needed.

Sometimes it's a redundant stand-in for "body > .content" or similar (eg: divs dropped directly in body) - and is prevalent because developers don't understand and care about css selectors (or there's that one person on the team that doesn't -- don't get me wrong -- I realize the real world is full of real co-workers, and making a change isn't always easy).

And partially it can be an artifact of abusing floats for "grid layout". Most typically though, the "container div" just ends up being a completely redundant extra "body" element.