I've restored from my 6 backup, to my 6s.
I want to go "as new" but don't want to lose my year's worth of health data :-(
I want to go the "as new" route because my 6 was getting sluggish, delays opening apps, annoying imesage quick reply stutter, contacts not appearing for a second or two, and switching the phone on takes about 40 seconds compared to an "as new" 20 seconds.
I wish apple gave us a more customisable restore option - I'd love to be able to go as new, keep some app data, and health data. Ditch all the settings and other clutter.