It may well impact on battery life, however I carry a spare battery for my Samsung galaxy S5 so it doesn't matter much. I haven't noticed that it impacts on performance. I find it incredibly useful for example if I want to watch a YouTube video but also browse the net at the same time, or if I want to type on a forum but need to find some information from another website. It's easy to have two browsers open on the same screen.
It's a feature that I'd love to have on my iPad Air, but perhaps not enough as I still choose an iPad over one of the galaxy tab pros.
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Well that's the advantage of having multiple devices lol my boyfriend can't understand why I can on occasion be using my iPad, iPod touch and smartphone simultaneously