This is a complex question.
Consider a 200 page book sold 2x ways...
1) Amazon: One time sale price of $20 - 30%.
2) Split 200 pages (at an average 200 words/page) split into 200 blog posts which generate profit/hour using either digital marketing + email marketing + direct mail marketing.
Let's say each page generates $1000/month income... so...
200 * $1000 == $200K/month income.
So $20/once verses $200K/month...
First question about book publishing is purpose of the book.
Tip: Smart Marketers never, ever, ever consider publishing a book for income.
There are many other reasons to publish.
Income is never a good reason for publishing.
Start with your profit/month, then number hours/week you'd like to work, then you'll generate a clear publishing path, along with your publishing calendar.
