Well, it was use in cutscenes like CJ shooting gangs makes it, AI controlled player, this will have Player 2 controll by AI to assist you but wanted level will still increase with AI Controlled Player 2's actions.

To start the action, type "peds" to make the second player kill random peds, if you type "peds" again, player 2 will stop killing any peds.

There's more commands for player 2:

easy = Kills only the player
team = Follow the player

Temper & Fire Rate Levels:

Hate1 = Too Easy Rate
Hate2 = Easy Rate
Hate3 = Normal Rate
Hate4 = Hard Rate
Hate5 = Very Hard Rate (Keeps shooting until reload)
Hate6 = Headshot Mode (It's on 0 but it's keeps shooting like very hard rate until reload)
Hate7 = One Shot Mode
Hate8 = Ultra Too Easy

You can make Player 2 switch weapons and sprint but you can't control his movements until there's no peds or disabled it when you use SAAC2.

You need: Improved 2-Player New Animations: http://www.gtainside.com/en/sanandreas/mods/107212-improved-2-player-model-selection-new-animations
Or
http://gtaforums.com/topic/874934-cleo-2-player-mode-enhancements/