A mirror-reversed set is a printed copy of your house, resulting in the same image you would see if you held the drawing up to a mirror. Everything, including the text, is backward in relation to the original design. These kinds of drawing are typically used to reorient an original plan more advantageously on a site, either because the homeowner prefers it that way or because of limitations of the site itself.
A Right Reading Reverse set is a True Reverse of the plan. The plans will be mirrored and text and dimensions are updated so they are not backwards.