[wups]

It's been discussed multiple times, nowadays there are two-three disadvantages of this system.
First and most important - the aimhackers. You just can't detect them without an admin test.
the second would be the latency lags. People get desynced and you can't change their health by SetPlayerHealth, so they get reported by other players of being invulnerable.
And the last - you can't give grenade and rocketlauncher damage.