What does xfce4 power-manager do in "presentation mode"?

It does two things, both intended to keep automatic features from messing up a presentation where you don't touch the machine for a long time (e.g. a teacher showing a video to a class):

• Turns off DPMS (Display Power Management Signaling) so your screen won't blank or sleep
• Prevents screensaver mode from activating

It prevents your system from suspending or hibernating.