I'm not a proponent of auto or constant sync. I don't see the need to be constantly syncing, my pace of research doesn't merit syncing more than once a week.
Ancestry, for some reason I've never been able to get a logical answer to, maintains that auto-sync should always be enabled. I beg to differ, I've never used auto-sync and I never have the issues so many post about.
The Ancestry site has always had server issues, there was a long and recent bout over the holidays. Experienced users know to avoid Ancestry on the holidays, they offer free access, they drive hard to increase subscriptions, and people have more time on their hands to be on the site.
It's best to be aware of how the site is functioning before syncing. I'm simply detailing what is working for me. There's vast room for improvement on Ancestry's part, but I get the most out of the service by being aware and learning how to work around the wonky.