You might explicate them in the assignment, in peer review or conferencing, and in your evaluation sheets. Save time by supplementing your written comments with peer review and Five Minute Workshops, but guide those discussions so that they stay focused on the most important issues. They can save you time. Assignment-specific scoring guides pose less of a problem. Usually, the more closely tailored the scoring guide is to the assignment, the better it is.
Students benefit immensely from close commenting.
Both conceptual and editorial comments help the student learn the course material and hone their writing skills. Unless you write some summary comments to establish priorities, your students might attach too much importance to minor asides and not enough importance to critical issues. You might limit yourself to summary comments so that you are selective and focused. You might look only for patterns of error in editing.