Also another factor is whether informing an individual of the rightness or wrongness of a choice will have a positive impact on the situation.
Pragmatism is one of my key values so when I speak I want it to have the most impact. My mind tells me what people or doing wrong constantly. Their is little point in telling someone what they are doing wrong just so you can later say "I told you so". Often using discretion, cause and effect analysis and a value hierarchy will assist one on when it is time to speak up.
Too much and you just become a nag and a 'kill joy' and worse your words have less individual impact. Too less and you become apathetic or even negligent by omission (or even guilty by association). Like most things 'moderation' or a healthy balance as well as case by case analysis is best.