Seriously- you need to turn both of them off-
it doesnt affect overall performance
its causes glitchiness on playback-
you dont want anything reading the discs at all while you are playing back movies
file sharing has constant background disc activity - which does affect playback
and screen sharing captures the entire screens and transmits it over the network.
And quite honestly this is a really bad idea when you are trying to maximise graphics performance
you really really dont want either of these activities going on in shows - ever
Even spotlight needs to be turned off- you dont want the discs being indexed either