I was told that after each application I need to scuff the service with fine sand paper, clean it, and then apply the next layer. Is that true?

Thanks

Only if you want a dust free good looking final product. When you apply poly the first coat raises the grain a tiny bit and you need to knock that off before the second coat. The second coats pretty much solves the grain issue, about 75% but bits of dust also get into the poly and you need to make the finish etched so the next coat can bit into the previous coat. If you are working on something that will not be touched and will be several feet away from view you can get away with skipping these steps, it will stick together.

Thanks again.