A OneNote notebook is comprised of separate files, which may be stored in different locations. Sure, if you first create a new "Section" in OneNote itself, the application will create the new file in the default path (which can be customised via Tools/Options/Open and Save). But you can easily move that file elsewhere once it's been created. Just create a normal Windows link to the file in your notebook folder and OneNote will show the tab with a small symbol on it, so you know that file is not physically part of your default notebook.

This feature has many uses: I use it to link project-oriented OneNote files, that are stored in a directory managed by source code version control, into my main notebook, for example. I also have some files that are stored on a network drive, and that's where I recently found a problem: While searching my notebook for a string I knew had to be there somewhere, I found that OneNote doesn't include network-stored files in its search by default. They call that feature "performance enhancement" :-) Well, I found the place where I could switch an option and now things work fine. Can't help but wonder though, with shared sessions working as well as they do, even over WAN connections, does searching a file on a network drive (which will be on a fast connection, more often than not) really create the kind of load that needs to be optimised?