I think, like a lot of things, it depends.
A good example where I think it’s important to cite a reputable source is this question about defrag’ing a Mac’s hard drive.
@richardhenry could’ve just explained that the Mac auto-defrags the files it needs to… but that might’ve left the door open to misinterpretation. There are third-party apps out there that will defrag a Mac’s hard drive. So, someone might mistakenly think that hey, if there’s something to buy, it must do the job better than for free. (And if you’re talking about Windows and it’s built-in defrag tool, you’d be right).
The citation itself lends a certain gravity to the statement as well as context.
Done improperly, messing with one’s hard drive incorrectly can lead to data loss. Not something you’d want to be cavalier about.
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And like @wildflower sagely suggests, it is also important to point out one’s guesses as such. And make your experience in that area known, too. A professional or expert guess is a good thing to have.
I’ve found though, that in the cases where I might attempt an expert guess at something, that I almost always can provide a citation anyway.