As an industrial designer, much of my sketch editing is to tweak a contour in relation to where it was before. You know... I need the contour to be thinner here, bulge out more there, etc. For years I have been using the following technique to create a reference for tweaking, so I know what the curve looked like before I started messing with it. I will highlight a sketch I wish to edit, CTRL+C (copy) it then Ctrl+V (paste) onto the plane the sketch was originally created on. Then I will drag the copy up the tree to a position above the sketch I wish to tweak, so I can use the copy as a reference when editing the original
If the sketch is on a model face, copying and pasting is less robust - a sketch pasted on to a model face will rarely be in the same position as the original. In those cases, I will start a sketch (on a plknae if I can!), then convert the edges of the original into the new sketch. Then I go to display/delete relations and delete all external relations, which will allow this new sketch to be dragged above its original parent. But of course I mostly create sketches on planes, so the need for this is pretty infrequent
But what about 3-D sketches? We can't copy and paste those, can we (not a rhetorical question - I really do not know for sure). Since I can't identify a way to copy and paste a 3-d sketch, I will instead start a new 3-d sketch, convert the edges of the first 3-d sketch into the new one, then go to display/delete relations and delete all the relations. I can then close out, and I have a perfectly safe copy of the original 3-D sketch that I can drag up the tree to use as a reference for tweaking the original.
An extra bonus to getting in the habit of creating reference copies before editing sketches - if you edit a sketch and close out of it, you lose the ability to undo your changes. By having a reference copy of the sketch from before it was edited, you will have a template for returning the model to its prior state if you learn things were better off before you started editing. Its also nice to be able to have a revision history of some key sketches in models. I don't know about you folks, but I really like working with a net when I can!