So right now I was improving my Sherbet Land course time, and because I've improved as a player since I last played the level, I got a new record pretty quickly, but unfortunately I forgot to save the ghost (though I have the video recorded). While I had what's important, I was unsatisfied having my saved ghost be much worse than my record, so although I got a decent time, I had to improve it again. Unfortunately, I couldn't seem to do this and usually restarted as I was always behind my sloppier ghost.

Eventually I had a clean second lap, which was my best lap as I hadn't spent time improving it either. I had to finish the race for once, then I saw "Save Ghost" in the menu, and lo and behold, it was my better ghost! I didn't know this about Double Dash, and I honestly think it's an amazing feature! So I had my better ghost saved and then realized, I hadn't been playing badly, I've just been racing my better ghost! So with a sudden burst of motivation, the very next attempt got me a new lap time in both 1st and 2nd laps, and then I broke my record again.

But it's not Expert yet, so I'm still not finished.  

that's why you go to options and turn ghosts off  

i have never used it maybe early when the game was released!

I too never race against a ghost, but I do want to save ghosts of my PRs, so that I can use it to try and figure out where I'm losing time, or if some change in strat saves time. Annoyingly, if you disable ghosts, you can't save them either.