One of the strengths I’ve found in OneNote is the ability to have multiple notebooks. Now I know you’re saying, “but Evernote does that!” The difference is that OneNote notebooks are separate files. They can be selectively opened and closed as needed. If you’re building an informational archive you may not need access to the notes you took on a trip three years ago, but may still want to get to them at some point, the multiple notebook model makes it easy.
A practical example
One example of this is I have created notebooks for each of my previous jobs and moved to those notebooks all the emails, contacts, and other information for those companies. The benefit is that I don’t need to open these notebooks nor do I need to have them synced all the time. They’re accessible when I need them, but not tying up storage on my mobile devices.