I find Ancestry.com generally useful, but things others put there need to be taken with a HUGE grain of salt. You can't take everything as being totally accurate.
I have my family tree back to my g-g-grandparents all the way around. I have birth, marriage, and death records on many items to support my tree. On Ancestry.com I find numerous careless or outright wrong errors, that could lead to all sorts of far-reaching errors. A misread document due to someone's sloppy handwriting can result in incorrect connections being made.
Case in point: My Mother's maiden name starts with the letters "Pu." Someone, somewhere, misread it as "Ri." (Try writing those letters as a capital P, lowercase u, and then capital R and lowercase i, and it's easy to see how it could get messed up.) But then they put her misspelled last name into a published family tree book, which went genealogically "viral." I see her mentioned all over the place with the wrong name. And there's no way to correct it.
So as I was entering my family tree data on Ancestry.com, and enter my father's name, it wants to connect me with family trees with him marrying the wrong woman. (They later divorced, so I guess maybe it was fortuitious... LOL!)
My issue with that is if there are facts that I KNOW are wrong, how can I trust what I see that I may NOT know about?
Dave