The skins are tough and don't break down into the sauce. The seeds can be unsightly and annoying to people with dentures. When I make my sauce for the freezer or even to eat right away, I put the tomatoes whole into the freezer until they are solid. Then you run them under warm water, rub with your fingers and the skins just slip away. I just ignore the seeds. 'Course, my sister is about to get full dentures, so she may care.