If, by switched off, you mean you are done with your computing session and don't need anything to be in "sleep" mode, then yes you can stick a power strip or other on/off method in front of both the PC and the monitor, and turn them off (after a proper OS shutdown). Should be no watts drawn at that point.
If they are in "sleep" mode, per your power settings in the OS, then you might not want to kill power to the SMPS power blocks or your PSU.
Both of those are switched mode power supplies (SMPS), which in most cases is always consuming/messing with the AC mains power, unless you have an on/off switch in front of them. Either by power strip with on/off switches, or by on/off switch blocks, I power off most of these when the device behind the SMPS isn't in use. I hope this cuts down on THD in the house wiring ...
Hope this helps ...