​You could say the purpose of feedback is either to improve confidence or improve competence, with the first being 'positive' and the second 'negative' feedback. But it's probably more helpful to say that the real purpose is to make people aware of something they are currently not aware of. That might be the impact that they are having or the specific actions / words that are causing the impact (either positive or negative). Giving people more awareness is always helpful (positive). 

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The best-known model is SBI (or SAID) but, because I like to start with the impact, I use I SAW.  

I  = Impact: Explain the impact... on you (I was happy or got irritated), or others (they got engaged or they got bored), or the business (we saved a lot of time / money or we lost a lot of time / money).

SAW = Specific Actions / Words: Reference a specific situation or specific moment in a meeting - don't talk in generalities. Even if giving feedback on a habit, pick an easy to recall example. Be very precise: What did they do (not do) or say (not say) that created the impact? 

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​One hint. Point your finger at the impact - NOT at the person. If you point a finger at someone, it will always be seen as a 'threat' - triggering 'defensive' reactions, and switching off the Pre-Frontal Cortex (PFC), the only part of the brain which can use feedback to make intentional change.