Part of the reason for publishing books myself is I want full control from beginning to end. Sure, I could hand this off to someone and hope they don’t leave out a chapter. When I use Vellum, I know my book is going to be exactly what I want. Vellum generates ebooks ready to upload for Amazon, Apple, Barnes and Noble, Google Play and Kobo. There’s an add-on you can purchase to create print-ready pdfs that I use for Amazon’s KDP, and Ingram Spark. They’ve never been rejected for poor formatting.