For many events it is useful to display pairings, but not allow players to start their games just yet.
Draft – An arbiter can see the pairings and edit them, but players and spectators in the Event Lobby do not see anything about this round. You can even ‘hide’ a round mid-way through the Event.
Published – Pairings are visible in the Event Lobby but there is no Play now button, so players may see their opponent’s from the Round tab, but not start their games.
Live – As soon as the arbiter changes the State to Live, the Play now button is displayed in the Lobby and players can start their games.
See the situation from Arbiters' view and Players' view: