Basic things like being able to attach sources to data points (like birthday) at time of creation.
It's run by the LDS Church, so there's a religious tone to their marketing. But you don't have to be a member or religious to use it.
But on the other hand, I was just a minute ago wishing that this sort of service existed publicly as a Wikipedia-like free resource, which is a strict superset of the LDS Church having it, so maybe that's unfair.
https://www.familysearch.org/en/help/helpcenter/article/what...
And I should also point out that the Church issued an apology for that particular incident, as well.
One challenge with an authoritative tree is when a distant or non-relative creates a profile, marks it living and then that creator disappears.
A close relative shows up but the profile is locked to the creator. The actual relative has to jump thru hoops to get access to their own family.
With privacy concerns, I don't know how to handle it better. Only that folks might want to avoid creating living profiles except for close relatives.
But such a thing would probably have a bunch of abuse scenarios that would be hard to solve for (it's "what's your mother's maiden name" as a service, for one), and I'm not sure if they're easily solved. But it'd be really cool.