This point is purely coming from the experience I had from the iOS on my iPhone and to be honest, the pretty slick visuals had a real knock on effect in terms of performance. There were many points during the testing of the iOS where I was waiting around for my phone to respond because of the new operating system, and as of the iOS, it made several games near to unplayable due to the downturn in performance. The problem itself it likely to stem from the fact the phone that could handle the amount of processes it had on previous operating systems, was having a real tough time handling the combination of iOS 7 alongside multiple apps being opened. This alone had me frustrated, but there was more to come... During Beta 4, my phone would go through a stage of turning itself off around 4-5 times a day, and when a new app or action was executed on the phone, the same would happen. There are many reasons to why this problem may happen, but I think it came down to the processor taking too much and crashing. To emphasise on that point, my iPhone never crashed once on iOS 6 during the 2 or so years I was using it, but maybe on a more modern model there was no such problem in terms of crashes.