Depends on when and how you use your N7...
If I going to use it soon then just press the power button once to lock and put the N7 into standby mode, press power button again to unlock and wake your N7.
If your not going to use it for a while, like over night etc then long press the power button to bring up the power menu and select Power off to turn your N7 off.
Ultimately it's up to you the user but this is how I use my N7.