1. What are the benefits of creating an "app" and not simply converting my book to an eBook?
When you convert a book to ePub, it will convert in to a single package of continuous text and images. On eReader devices, a "page" is simply the amount of content that will fit on a single screen, which will vary depending on your reader's device. Think of it in terms of a single Web page. Part of converting to ePub involves removing much of the printed page-based formatting (page numbers, headers and footers, page breaks, etc.). These are irrelevant in the eReading context.
However when an app is created for a book, additional features can be added such as "zoom in/ zoom out to allow large tables, chart and illustrations to be viewed at the full size of the tablet's screen, in color. Audio and video tracks as well as animation can be embedded to make it more vital. Additional search capabilities and other features are also available.