I definitely would do that if I could. I would absolutely love to tell it to only charge to 66% (or whatever, even 50% would work). I rarely use the phone for multiple hours at a time without access to power, and when I do, I usually know beforehand (like during a trip or something) so I could tell it to charge all the way. My battery rarely goes below 80%, even now that the phone is 3.5 years old.

I understand newer iphones now have the option to only charge up to a certain percentage. Mine doesn't have that, it only has the "smart charging", which tries not to charge it too quickly and only is full by the time it expects you'll use it (usually in the morning). It's very hit and miss for my use patterns, so it ends up at 100% most of the time...