Sometimes I avoid using online trees, GedCom files, etc. for as long as possible--avoiding them completely if I can.
I'm working on a family of my wife's in Missouri and there are online files about this family, but most have the same gaps that I do and others repeat undocumented claims made by researchers decades ago. In this family, I'm finding that a better use of my time is to review original materials (or digital copies of them) and really research the family from scratch. Going through the compilations of others was not getting me anywhere and seemed to be an ineffective use of time.
There are times where I have used online trees to get good suggestions or leads. This family (which I won't name), just isn't one of those times. When tree after tree repeats the exact same information without sources, it may be time to go back to the drawing board.