When proofreading, I keep comments to a minimum, only commenting on punctuation that affects the whole manuscript. Certain things I don’t comment on, such as a missing set of speech marks, I’ll mark it up using track changes without leaving a comment.

For copyediting, I will leave a few more comments, for example, if I’ve deleted or rephrased a sentence because of repetition and there is not a stylistic reason to keep the repeated line.

For beta reading, I’ll leave the most comments, for example if there are inconsistencies in characterisation or plot.

For all types of editing, I will leave comments on aspects that are particularly effective or evocative. It is worth repeating that there is always a level of subjectivity to comments and the author is free to accept or reject the suggestions as they see fit.