As was stated above, many profiles that have 10 citations for each 'fact' has come from a Gedcom, but you can also find half a dozen 'different' sources on family search for a marriage. Some might have different spellings, different dates (marriage intention vs actual marriage date), different locations (spouse lived in different areas, so both are sourced), some have one or both parents of each person, different spellings of one or both names, etc. Those are all valid, to me, because if you only put one or two, and those disappear, you could have nothing, but when they have different information, it is important to have them.
I have seen multiple birth sources for similar reasons because some may have no parents, one parent, or both parents.
Personally, I don't put census as a source for birth, other than the 1900 census since it has month and year of birth and that would only be when there is no existing primary birth source. That census also has approximate date of marriage, so if no source exists for marriage, it is a source.