I think you should only ever give freecards if you're two cards ahead of your opponents, or you're a certainty to win the hand. for example if you hit high trips on the flop or turn, even if you're opponent has two-pair, they will need runner-runner to beat you. Then when you push all-in at the river, they will call your "bluff".
Another great time to give free cards is when you flop a boat or the nut-flush and other players are quite-obviously drawing. Nothing sweeter than seeing four cards to a straight or flush when you flopped a full-house. Well maybe something sweeter, but I'll keep this post clean
