Not just for starting over, scraping the surface of a painting is also a means of controlling texture in preparation of additional layers.
I met an artist on a recent plein air excursion who expressed surprise and disappointment that I had scraped a painting back that I was unhappy with so that I could start again fresh. As if I had committed a deep sin that wounded the soul and "Spirit of Plein Air" . . . Yada Yada.
I chose oils precisely for their forgiveness, because I could start over. I also like the idea that I can erase entire passages from a painting and re-state it. I like that about oils. It's not a sin, it's a strength.
I don't know where this attitude came from. I see the shock on the faces of the general public, so maybe it came from a system that teaches our children that starting over is somehow a fault. It's not my place to debate that. . . I'm an artist not a social scientist. I'm a failed artist among other failed artists who go back hundreds of years, who happily scrape their paintings so that we can make better ones.