The hashtag is not very much important for Facebook but Hashtag is highly recommended for Twitter and Google Plus to increase your visibility. Thanks.
It is a difference in intent, I think. There are a lot of Facebook users that value privacy and do not want their posts to be discoverable. I definitely think it is foolish for businesses to not at least throw 2-3 relevant ones in it.
I use hashtags on facebook only if I feel like it. I think hashtags are preferably on Twitter and Instagram only.
Hashtags are a Twitter and Instagram thing. Using a hashtag on Facebook makes you look kind of 'out-of-date'
I think for business it won't do any harm to put one or few related hashtags. Why not? Over time it might bring some targeted traffic. Better than nothing.
No One, I don't think the same as you, there are many who use the hashtag and there are many users who don't know the exact meaning of hashtags but keep using it on FB, so how you can say that there is no one who uses the hashtag on FB. If you do the Case Study on it so kindly share with us.