Any good evaluation focuses on what an individual is doing well (strengths) but equally important is looking at areas that are in need of improvement (weaknesses). Done right, a good evaluation becomes a personal improvement plan for the individual as well as the organization they serve. The key if providing concrete examples and allowing the individual to question or get clarification to ensure understanding.
Many leaders find this uncomfortable and as a result shy away from this important task; however, the performance will continue to suffer along with the missed opportunity for the needed improvement. Likewise when a reviewer softens the intent or lightens the degree of response, they allow the individual a false sense of security or even worse reinforce the negative or sub par performance.
In a cost benefit analysis, we refer to this as an opportunity cost, in human resource management it is a lost opportunity to strengthen the team.
“I think it’s important to actively seek out and listen carefully to negative feedback. This is something that people tend to avoid because it’s painful, but I think this is a very common mistake.” - Elon Musk
https://medium.com/science-journal/the-importance-of-negative-feedback-5dec045232bf