Why do business social network users?

The issue of business social networks has repeatedly and for quite a long time been raised on Habré.
If the reason why networks may be needed by a business is fairly obvious, then it’s not so clear to users ’needs.
The following needs come to mind:

• find out about news, discounts and special offers of companies of interest . The need is clear enough - but at the same time only a few people will be actively engaged in it. And most of them are already solving them somewhere. You can become an aggregator of companies' offers - but rather it is functional for an RSS reader, rather than a social network.
• read reviews about the company . The thing is necessary - this is confirmed by research ( Western , of course ( link to marc in Russian )). A potential motive for writing reviews on a large network is to have a large user rating. But this is also not necessary for many - as always, there are 10 viewers for 1 generating feedback. Better than the available resources, this can only be because the reviews on everything that can be collected on one resource - but this is also a minus, as now the reviews are scattered on thematic portals to which people are already used
• participate in thematic communities . All this is already in one form or another, and it is rather difficult, if possible, to lure users from the forums and communities they are used to without giving anything fundamentally new.
• Ask the company a question (communicate directly with its representative) . Do you really need the Internet for this - when is it most often possible to make a phone call?
• learn new reviews of users you trust (reviews of which you have already read before) . The need is non-standard, but most often for this purpose just friends and acquaintances are usually used (if from the network - then some other.
• find out the overall rating of the company / place of the company in the rating . Another is not the most influencing decision making need.

Such a point of view may seem depressive-decadent - I just try to approach the reality of each need critically.
Total we get the conclusion: business social networks - stillborn idea, which is not implemented because it does not satisfy any unresolved user needs?

I invite to discussion those who raised this question earlier - Yuri yurylifshits , Anatoly amilner , Vyacheslav slava7