Citations, fact checking, and minor corrections are EXCELLENT things to leave for others, or for later review by yourself.
Leaving citations for someone else is complete nonsense. It shows that you didn't understand the paragraph of mine you quoted. A citation says where you got the source from. If you write and article, and then I come along, I have no idea where you got the source from, it is impossible for me to add the citation. I can add a link to somewhere that says the same thing, but that's not citing sources, because whatever I link to probably wasn't actually the source. Me adding sources to your article is basically me rewriting the article - your work becomes nothing more than copyediting that happened to be done before I wrote the article (and yes, that doesn't make sense - that's the point I'm trying to make).