I agree in general; 'I told you so and it's your fault' doesn't help a relationship in crisis. But ... It can compel some attention and provide an opportunity

I agree in general; 'I told you so and it's your fault' doesn't help a relationship in crisis. But ... It can compel some attention and provide an opportunity for extra thought. An unwanted verbal message over lunch is easily forgotten or misremembered, intentionally or not, weeks or months later. A written one is harder to ignore and provides something the recipient can re-read and ponder later. Also, there are circumstances where documentation is good to have. For example, it may help in a company with more layers; your email to the guy 2 layers up may help when the guy 4 layers up gets involved.