Difference Between controller and controller.content

Difference Between controller and controller.content

I have an ArrayController and was using {{#each item in controller}} to
iterate over the items in the controller. This was working fine while
using the same controller however after switching controllers I ran into
some weird behavior which stopped the items to being rerendered. Switching
to {{#each item in controller.content}} solved this problem. However I am
not sure how this even happened.
What's the difference between controller and controller.content in an each
expression (or any where else).