This question is a little vague without context.  I'm going to answer based on the idea that people on this service are trying to sell something.  It might be a service or product but their end goal is to obtain customers.  Some might be here to find other employment opportunities or other reasons but most are attempting to expand their business.  

The goal of a site like this is to explain to people what you do and hopefully confer a reasonable feeling of skill or quality so others will consider you when needing the product you offer.  It also gives you a chance to meet people you otherwise wouldn't simply to expand your brand awareness.  A person needs to be aware though that networking is not an end in itself and lots of time and money can be wasted just communicating with others that don't have a use for what you do.  Always remember to ask for the sale.  Or at least a referral to someone who might buy.