J, perhaps in theory you only end up with one tree so long as the records stick with the person. But when the 1800 census that represents a person is linked to one set of parents and the 1810 census is linked to another set of parents, FS assumes that the person in the two census records is a different person. I have encounted before on FS two and three trees for the same person. On WT, you initiate a merge. On FS, I have disconnected parents, added the correct parents, only to come back a week later and find my changes reversed.
The biggest problem I find with Family Searches user introduced information is that it is a huge free-for-all. If you get someone who is in love with their fantasy lineage, there is nothing you can do to introduce fact save for re-uploading your work every week.
Edit to add: I just tried adding new people as spouses and parents of people in the FS "tree" and it let me enter them, no source needed. So if I go and add an ancestor, and call him George Washington, and give him the same birth date as the American Founding Father, we will have now two Washingtons. I can then add parents or grandparents and they don't necessarily have to be the correct parents.
And this is what I see on FS, with great regularity, two or three parallel trees, all unsourced, all different, and all member generated.