Well, after using the facility to prevent apps running in the background (repeatedly), I've reduced usage to 100% in 12 hours to 60% a day - better than before, so a throughgoing win. I still have all aps that I want - eMail, whatsapp etc - running, just killed the stuff that has no business doing anything when I'm not looking at it; fantastic endorsement of the Google development roadmap.
By the way, it doesn't kill the apps in the background, just prevents them from doing anything. Bring them back to the foreground and refresh if needed for full functionality/