The amount of editing is dependent upon how the work was written, how appropriate the English expression is, and what other matters (such as Table of Contents, cross checking citation/references in academic works etc) need attending to in order to produce a professional looking finished product.
The level of editing is a choice that you should make, bearing in mind the cost, the time and the quality of the finished job that you desire. Do you just want there to be no errors? Do you want to make sure that the English expression is most appropriate for the target audience? Or would you like to ensure the document structure conveys your ideas most clearly and with relevant presentation of graphics, tables, lists etc?
Halcyon Words will advise and help you in making the decision that is best for you.