Posted by Grant Richardson, 21st May, 2015
Either, but it depends on the situation.
To put a device (such as a mobile, tablet or computer) through its longer process until it turns off completely, you should use:
On the other hand, if you simply want to put the device into a “sleep” mode (meaning that the device’s software is running but the screen is off), because you don’t need to interact with it at that time, you can use either:
There is no difference in meaning between the two.
In certain situations, such as at the beginning of a lesson or before watching a movie in a cinema, you might be given an announcement to
Please switch off your mobile phone
Of course, here, it means to put the phone into a state so that it won’t disturb others or yourself — silent mode, or shut it down, and NOT simply switching the screen off and leaving it in vibration mode or leaving the ringer on, unless you don’t mind being asked to “turn it off” again each time it rings, beeps or buzzes.