Since the purchase on 24.03.2016 the hardware has not yet made any problems. Should that change, I document it here.
My iPhone I usually turn off never, but use it always discreet (am not a "Smartphone Zombie") ...
At night, I do not expect any calls, so I turn it then in airplane mode, which consumes a maximum of 2% energy.
The operating system on my iPhone 6s Plus runs completely trouble-free (initially iOS 9.x and 10.x now).
Here I write down all reboots with justification, to give you an idea of the reliability.
24.03.2016: First setting and software update to iOS version 9.3
19:24 Uhr: For the first time turned on. 19:26 it puts the statistics: Settings / Mobile Network.
22:57 Uhr: Restart after updating to iOS 9.3, System Build 13E234, kernel Darwin Kernel 15.4.0 Build 199506.
18.05.2016: Software upgrade to iOS 9.3.2
23:26 Uhr: Update via iTunes with iPhone's USB cable lasted seven minutes.
07.06.2016: I turn off the iPhone first time
22:18 Uhr: Because of access issues on the 2nd mailbox folder I turn off the iPhone first time.
22:29 Uhr: Boot time with Unlock iPhone and SIM card lasts until 22:30, then it is ready for use again.
22:30 Uhr: The mail folder of the 2nd mailbox are fully available again. The restart was worth it.
26.08.2016: Software update to iOS 9.3.5
23:08 Uhr: Restart after update via iTunes with iPhone's USB cable - took one hour with download.
Next page: Informations about Firmware and Operating System Apple iOS ...