I'm assuming you're speaking about translation so forgive me if I'm wrong, but as someone who has done both editing and now primarily provides first pass translation, I think the main role of an editor is to have a strong vision and make sure that vision is coming across in the work you're overseeing. I will admit that stances on this differ from editor to editor, however. As an editor, I was someone who tended to smooth out the text I recieved (if needed) to ensure the text was both interesting and true to the original intent. Some editors rather leave that work entirely in the hands of the translator (and I do think, at the end of the day, it should mainly be there), but as the person in charge of the final product I do think the editor needs to both know and take responsibility for how it comes out, and that requires a strong vision and the ability to trust and guide translators towards that vision. (I'm running out of space so I'll include the rest in the thread)