We have my iPhone, iPad Air, iPad Mini, and an iPad 2 my mother is using, all with the same Apple ID. It is great because we all share the apps. My husband has email set on the mini he uses and I have the emails we both use set up on my Air, I have the iPad 2 that I am letting my mother use set up with her email address (she no longer does the email anyway). I have restrictions set up on the iPad 2 and load and delete apps turned off, as well as any settings I could think of, this way I am not worried some niece, nephew or wise guy brother will go over and mess things up. Works great. With the apps turned off, nobody can update it to 7.1. She is going to be 90 in August and the little changes in 7.1 would confuse her, so as long as she is using the pad for her card games and looking at photos, I am not updating it behind the last 6.whatever version. So, multiple devices works quite well.
I can locate all the devices with the fine my iPhpne app.
I am sure this sharing would not work for every situation, but for us, it is great.