I have only contacted two people about my Lippman great great grandfather. All over Ancestry, people have him married to two different women simultaneously, fathering children with each in alternate years. I did get this corrected, but otherwise, I leave it alone.
On the other hand, I have found mistakes in other trees to sometimes give clues that are worth exploring. For instance, all over Ancestry, there are trees that say my Lock clan comes from Gruzdiske, Lithuania. I've had relatives tell me we come from Zagare, 60 miles away. When I went looking for a town that sounds like Gruzdiske but is near Zagare, up popped Gruzdziai, which records show is the correct town.
Another incorrect but useful factoid - All over Ancestry there are trees that show a certain Alex/Elias Lak/Locke was born in Riga, Latvia. His own census records say he was born in either Germany, Estonia, or Russia. But I figured maybe it is worth checking to see if there are any Lak records in Riga. And up pops several records showing a known great uncle Jacob Lak/Locke living there for several years before immigrating with his family to Boston, US. This was something we never knew about. Checking the naturalization papers for his children, shows them saying they were born in Riga. So, the trees have the wrong Lak/Locke born in Riga, but checking this out led to other correct Lockes. As it turns out, Alex/Elias Lak/Locke was born in Telsiai, Lithuania. HIs family moved to Estonia for several years, prior to immigrating to Chicago.
So, others' mistakes can be useful. However, I don't much bother trying to clean up these useful mistakes, since I figure the tree owners won't much care. It's a free country, and they can do as they please.
Lak/Lok/Liak/Lock and Kalon/Kolon in Zagare/Joniskis/Gruzdziai, Lithuania
Lak/Lok/Liak/Lock in Plunge/Telsiai in Lithuania
Trisinsky/Trushinsky/Sturisky and Leybman in Dotnuva, Lithuania
Olitsky in Alytus, Suwalki, Poland/Lithuania
Gutman/Goodman in Czestochowa, Poland
Lavine/Lev/Lew in Trenton, New Jersey and Lida/Vilna gub., Belarus