Like everyone else, students respond to encouragement and positive reinforcement. When papers are smeared with red ink, even the hardiest ego can be slow to recover. Sam Dragga and Frances Zak have argued that we should provide solely positive responses, and the work of learning theorists supports the assumption that we are most inclined to learn more when we are rewarded for positive behaviors as opposed to being punished for negative behaviors. Students are not professional copy editors, and past research indicates that they don't appear to understand or respond to our abbreviations. Omit grades on individual papers.
Grades often transform the effective coaching role of a teacher to that of a judge and gatekeeper.
For example, in my experience teaching undergraduate writing courses, I have found that not providing grades can be incredibly stressful for students, and colleagues have reported similar results. And even though I wholeheartedly agree with being positive when responding to students' work, I believe we need to show students why some passages are weaker than others.