Obviously the impact of a soldier promoted into the wrong position can be devastating to the effectiveness of a unit. The impact of a less qualified soldier being promoted is devastating to an individual's morale and unit morale. Whenever you are tasked with writing an evaluation it becomes your responsibility to accurately document the accomplishments of the soldier. The evaluation provides important feedback to the soldier and is also the basis on which the soldier is judged by a promotion board. Evaluations must describe a soldier's accomplishments.
Quantitative remarks are the most effective.
Probably most important are comments regarding potential. Soldiers excelling in their present position deserve a comment identifying them as having the potential to serve in a position of greater responsibiliy.