"One Paragraph, Three Ways" touched on a big issue I have while informally editing friend's papers: maintaining the author's style. When I come across sentences that are poorly written or that I feel need to be rewritten altogether, it is extremely hard for me not to impose my own style. This becomes especially difficult if I run into many sentences that fit this description.
Obviously this applies more in a teaching scenario, as opposed to a professional copyediting setting. However, I am curious as to how to best edit a paper in this situation.