There are way too many examples of great composers/writers working on a piece for months and years in some cases for me to believe it’s a flawed concept for everyone to revisit or work slower. Also, plenty kept notebooks of ideas only to finish or develop them years later. If this advice was taken, who knows how many would have thrown away their best ideas and art. If your goal doesn’t involve lots of quantity and deadlines then I can’t say I agree with it either. Not every piece is meant to be written the moment you conceive of it. Some of arts greatest works took an extended time to realize. I think it’s better in the beginning to save your ideas. Accept they won’t all be good. At the same time, learning how to work quickly is a skill to aim for as well...and those tactics might come in handy for that. Not all composers work alike. I saw a guys video recently where he had a big box beside his piano. When he worked on a commission, he just wrote on paper and put his ideas in that box. He’d go back through it keeping all that worked. It was a huge stack of paper full of short ideas.