I'm redoing a decade old song as we speak. it's not on SC or anywhere but it's one of my favs of mine and I'm adding RT's I didn't have then.
These days I do whatever moves me. If it's a new song idea I want to finish while I'm in the zone, I do that. If it's a remix and new arrangement of an old song I get excited about then I do that. As long as it moves me and I'm doing something creative I'm not wasting time.
Now if someone said you MUST choose only one, I'd write, arrange and record a rough demo - what you're calling a "sketch" and leave the real mixing/mastering to somebody else but I don't have the luxury of that choice. Thank God with RT's I don't have to play a thing.
