Not so long ago, editors worked on hard copy, so a manuscript was treated with kid gloves. Can you imagine losing or damaging the only copy of a text? Not a fun conversation to have with your client.
But handling files effectively is important today, too. Save the original file, and back it up. If the file is long or made up of chapters, it’s best to save each part or chapter separately within a folder. When you’re ready to edit, open the file and rename it so that you’re working on a duplicate, not on the original.
I’m sure there are some lost-manuscript horror stories out there. Thankfully, the only thing to worry about losing in this day and age is face. But who wants to look irresponsible and unorganized by asking for files to be re-sent?