Hi dalyer. Sorry for late answer, I was a bit busy.
You're right, I do not make many calls, neither use phone for gaming or movie watching, intensively browsing (stupid idea to do it on 4" screen, if I have 15" and 24" available, right?) or any another battery consuming activity. I have phone mostly "to be available and when I need to call or text". I know, for such simply reason it would enough dumb non-smartphone, half size and weight, cost 30Eur and stay ready for week or more.
But sometimes I need to check emails, also using phone for ebay trade, geocaching, using camera and some another apps. It's better to have one device for all those things, than buy more devices just for exact use.
I decided to wipe built-in mod because was full of vodafone and other crap, constantly running and not possible to kill it.
It's also about lifestyle. For example, one of first thing, what I want to kill, was social apps, such a facebook or g+ and similar. I think people should live a priori real life and THEN share something interesting with friends or family, if it's worth it. And believe me, 90% of FB posts are worthless. People live virtual life and are trapped for checking status every couple minutes, who post what... Mostly because they have no idea how to turn off those apps (and be frank, most of them are not possible to turn off), so they get used to be "online" all the time.
I do not prefer same lifestyle attitude and even I don't like it, I must accept running facebook all the time. So I change mod and it's much better.
Besides lifestyle is also important, that I can't use phone in work. It's safety restriction, as we working with sensitive and valuable customer data, private things, accounts and credit card numbers and so on... So phone is switched to airplane mode and stored in locker room, almost full 8 hrs. During night also I don't need to be disturbed by anybody, by intention or mistake, so another 4-5 hours is again in airplane mode. That's huge saving of energy and even I have such settings with previous mod, not too much difference I get, because even in airplane mode many apps and processes running and consume energy.
I do not use any data, all data sync are via home or work wifi. I have prepay program, and it's quite enough for me, 25 euro charge can last for 2-3 months.
I hope it's good enough answer. If you need to know more, just let me know. :)