I use the online trees for the occasional clue when I am stuck as occasionally a tree compiler has stumbled upon a connection or a source that has eluded me. Those times are few and far between and are usually when I am really stuck.
And often when I am really, really stuck there’s not much in the online trees to actually help me because others are stuck on the exact same problem as well. But occasionally, for one reason or another, I have overlooked something or not located something because the information I have to work with is minimal, has key elements missing, or has an egregious spelling error that I think is correct.
But if the only source for a genealogical statement that A is the mother of B is an unsourced online tree, I’m not going to include that statement in my genealogical records. If there is no way I can evaluate the reliability of the statement, I’m not going to include it.
It doesn’t matter if I can cite it or not.
Others may disagree about including such information. But if I can’t tell who compiled it or where they got it and there is no way to evaluate it, I’m not going to include it in any compilation.