I tend not to concern myself with the battery and just use my phone.
My phone goes on charger at night with the screen on all night (nightstand clock with a black background). I get up at 5am and the phone is off charger until 10 or 11pm.
When I go to bed I have anywhere from 70-75% of battery left. But whatever percentage it is I put it on charger anyway at night.
I've done this for three years now. I did it with my 6+ for seven months, my iPhone 5 for two and a half years and a 3GS for nine months before that. I've never had any issues.
One of the popular battery apps tells me that my battery has 14% wear. I've been told that heat has an effect on battery, so I guess this is pretty good considering the phone has spent two summers of Phoenix, AZ heat going around in a car with no A/C and windows that are stuck closed.
All of this said, I don't use my phone like most people seem to do. Calls, texts, email and light web browsing.
I'm on iOS 9.0.2 if that matters to anyone. No CPU throttling due to battery.
EDIT: Oh yeah. My phone is never turned off (it's on 24/7). I cannot recall the last time I had to plug it in because the battery was too low.
My wife's 6+ is similar, but she uses her phone a bit more than I do.