The Alliance of Independent Authors has published a useful (and up-to-date) guide to the benefits of uploading books to both IngramSpark and Amazon KDP. Both services have their strengths, and combining them makes a lot of sense. Neither service has up-front charges or charges for updating book files (they make plenty from each book sold!)
One of the key quotes from the article:
Why You Must NOT Tick Expanded Distribution
This is one of the most common mistakes authors make. If you tick “Expanded Distribution” on KDP, Amazon makes your paperback available to bookstores and libraries through Ingram's network — but at a lower royalty rate (40% instead of 60%), and it will block you from publishing the same ISBN on IngramSpark.
If you plan to use both platforms: do not tick Expanded Distribution on KDP. Leave that box unchecked. IngramSpark will handle the bookstore and library distribution far more effectively, and you'll keep the higher KDP royalty rate for Amazon sales.