cause windowed mode is much better! you can switch to chats/firefox in 0,1 sec and back... fullwindow need 10 years to get back in the game... and with windowed you also can use skype and other progs as overlay :)
the most abuse windowed mode for overlay hacks and the most hacks only work in windowed mode so i think he want to use a hack
what kind of anticheat ? which server
darkguard > kill it @task
fairfight 2 > change the settings @.ini
other > idk :)