The pure system was implemented to prevent cheating. For example, some cheats may rely on editing the cgame.qvm to function. If pure is on, hackers cannot use the modified cgame.qvm. Same goes to models,textures and sounds. Super big models allow people to predict where the guy is. Transparent textures allow people to see through walls, wait, is this even possible without a shader? And you can make the sounds super loud so you can hear it wherever you are(of course if it is in your PVS)
