From TalentSmart --
"Too often in the workplace, punishment comes in the form of a public reprimand or berating, usually involving an impulsive and emotional response by an upset manager. This strategy may make the manager feel good, but it does little to reduce the chance of encountering the same behavior in the future. Instead, public scolding generates a stress response that prevents the offender from absorbing information. Principal Jim Sporleder of Lincoln High School utilizes a zone system (red, yellow, green) to identify when people are able to take in information that will help them to learn and improve. Lashing out at offenders puts them instantly into the red zone, if they aren't there already. It is thus vital to recognize when people are in the red zone, and to give them some time to calm down. Otherwise, your message will fall on deaf ears."
The green/yellow/red mental categorize is very useful for a lot of things, not just giving critical feedback. Assessing G/Y/R based on busyness/stress of prospects for selling also works well. Just mentally looking to categorize before taking a highly leveraged action -- selling, giving critical feedback -- goes a long way towards a performance boost.