Disadvantages of USB sockets
The biggest disadvantage is actually also an advantage, when there is no current being drawn through the USB outlets the USB socket turns off. What this means is that once you're phone or other mobile device is done charging the socket turns itself off thus saving energy.
The problem here is that once the USB socket is turned off the phone essentially believes the cable to be unplugged, the phone will then run on battery for a while, until such a time as the battery has dropped low enough that it begins charging again. What you then have is a situation where a mobile device is being charged many times through the night by tiny amounts. In the case of an iPhone this most likely means that all through the night the phone is going to be vibrating and beeping to confirm charging has begun (as iPhones like to do by default), and the vibration occurs even when in silent and "Do not Disturb" mode.