You never want to explain everything about all the docs you submit. You just need to explain any such info which you think it might be worth explaining. The things that can't be explained via those submitted docs themselves.
For example, if you are going to attach an affidavit, then you might want to explain why you are attaching one, etc.
Also, an LOE is not a mandatory doc, as such if you think that there is no such thing in your application that needs explanation, then you don't need to submit one.