My personal philosophy is to take the camera in your inventory that will get you the best pictures. An iPhone is easy enough that its always a backup if you need to put your other camera away for a bit, but you'll appreciate the quality of the dedicated device. I took my 10D everywhere with me. People said, "Aren't you worried about damaging or losing it?" Heck no. I bought it to take pictures. In order to take pictures, it has to be with me. Now that I have a 7DmII the 10D is in storage awaiting a trip where I need backup and the 7DmII follows me around.
(rant)
I understand that some people have different requirements. That's great for them. If its about the image... you do what you need to take the image. I am not a professional photographer, but I take my camera with me everywhere I go if it is at all feasible for me to take pictures. My coworkers were shocked that I started showing up every day with my camera bag. "You never brought that before!" they'd say, and ask "Why are you bringing a camera to work, you're an IT guy, not a photographer?" Thing is our lunches changed from being half-hour to a full hour. That means I have time to walk about and take pictures. They hadn't seen my camera before because I never had time to use it during a work day (but any event our staff participated in where pictures needed to be taken, my camera was there - they just failed to notice). My wife can't understand why I carry so much weight around. But its not a burden if you enjoy what you're doing. Anyone should be able to take a decent picture with almost any camera if its functioning properly and they have some skill. But that's not the point if the goal is the image.
If you feel that the best camera in your inventory is a "burden" for non-work photography - then your goal isn't the best image - its that simple. There is absolutely nothing wrong with that, either. For millions of people who have the luxury of being able to take images and have a choice in how they do it - their priority is not so much the quality but the convenience. For them, the best camera is the one that is at hand and is easily stowed or is attached to a device that does more than take pictures. You shouldn't have to lie to yourself to justify your decisions. If you have any regrets, do it different next time. Just like the people who are touting their favorite system because its small and lightweight. If its the only thing you got, great! If you bought it because that was your goal, outstanding. But if you're any kind of person who cares about the images they take, when you have your 5DmIII/7DmII/6D/etc in hand, you'll find yourself not minding the extra weight.
Something tells me the number of high-end systems Canon sells isn't going to be changed drastically by such opinions and goals. Their price might go up, but people who are looking for that capability will pay for it. Canon wins either way.
I'm probably going to get extra insurance on my 7DmII, its not all that terrible. I'm not really worried though. It can be stolen if people break into my house while I'm at work or on vacation - probably more easily than if its with me where I'm at. Maybe it will get me killed... but odds are, if I were to encounter such an individual without my camera being on me, I'd get killed over my S4 or wallet or just because they're having a bad day.
But really, the greatest threat to my camera was 10 year old Jimmy whose parents can't be bothered to watch and care about him while Jimmy takes things that belongs to others and smashes them to the ground. My camera had survived many adventures with me. But that... would have done it in if I hadn't caught it in time. Sometimes its not the unknowns that will get you, sometimes its a friend of the extended family that thinks they own everything in their vision that will do you in. And you don't even need to be on vacation for it to happen.
(/rant)