When I first got my iPad I wanted to start sync everything between it and my iPhone. I kind of wanted them to be a mirror of each other and always wanted to have access to all my data, independently on which device I used.
So I spent a lot of time to sync my devices so that they always had the same data. I did this for a while until I realized one thing.
I don't do the same tasks on each device.
Why then, should I spend time sync everything between them? I love reading books on my iPad. It has digital bookmarks, highlighting and a built-in dictionary. It's simply a great experience. But, I'm never gonna read a novel on my iPhone. The screen is way too small for that and I need to flip the page all the time. The experience is not that great here. So why then, do I need to have iBooks on my iPhone? Simple, I don't.
I don't need to spend all that time syncing books back and forth to a device I don't use for that task. It can be spent on better things. I read on my iPad, that's the only place my books needs to be. The same goes the other way around. I usually listen to podcasts when I take a walk. I don't carry around my iPad when I take a walk, so the podcasts doesn't need to be there. They should exist on my iPhone.
Every device has it's own purpose.
I never, ever create a web design or writing any code on my iOS devices. That's what my laptop is for. Instead of trying to do all sort of things on all of my devices, I give them certain roles so when I spend time with a device I know what kind of tasks it's best suited for.
My iPhone is a communication device. My iPad is a reading device. My laptop is a working device.