Audiobooks in iTunes and iphone

I listen to a lot of audiobooks on my phone. Typically, I rip the disks and then change the file type from music to audiobook and create a smart playlist to synch with my iPhone. When I connect the phone and look at the audiobook link, it gives me two options to select those to synch; 1. Audiobooks, and 2. Include audiobooks from playlists. Does anyone know the practical difference between these two choices? Which should I use? Thanks.