This is yet another question I get almost every time I pitch my services, and I've found a real-life example with which to answer it:
I know a nationwide, family-owned SME hardware business who feels very strongly that online anything is not a part of their business plan. Cool, power to you. Despite this, they do have a website, Twitter and Facebook. Their Twitter has 60 followers after 3 years of posting. They advertise sales every couple of weeks and have no shares, replies or mentions. Their website is simply a home page with their current flyer pasted on it - No search, product categories or available brands are listed. (I've looked at at least half a dozen of their SME competitors and all of them have made online purchasing available to their customers, and allow consumers to search their websites for the products they are actually interested in with visible stock, location and pricing information.)
I'll use my own brand's online presence as a comparison. I post to my social media accounts on a consistent basis (multiple times daily) and have 248 followers after 3 months of activity. On my Twitter I receive around 1500 - 2000 views a day. About 10% of the people seeing my tweets continue on to visit my website. If I was a retail marketplace like the company listed above, this would then be between 150 - 200 potential LEADS visiting my online store on a daily basis. Considering that this can be achieved by tweeting something relevant 3 times daily and having an engaging landing page for your website, your potential ROI here is insane. No bidding for billboards, newspaper pages or bench seats, and no drafting pages like with print ads (less time, less waste and less material expenses).
Because social media is sharable, you also have the perk of other people freely advertising for you when they find your posts engaging. Let's say someone shares your tweet, and that tweet reaches another 500 people via that other person's account page. Then 3 of those additional 500 people decide to re-share your post themselves, and you now have an additional 1500 impressions of your brand. If even 2% of those 500 new viewers decide to visit your website, that's another 10 views per share, per day that you are generating for your store for free.
Let's say the average tool purchase on this site would be a conservative $60 per customer. Think of the revenue this company could be generating that it is losing out on instead. Think of all of the cities and towns province-wide in British Columbia who have limited store fronts to purchase from but are expanding due to housing costs and the location of natural resources - They all have to truck in construction materials and tools and are a potential part of this company's online marketplace.
What marketplace is your company failing to reach? What are you currently spending per acquisition of new customers? Have you considered the cost of social media marketing as a comparison? (Do you need a quote?)
Business plans are not just about the money you are currently making, but also about the money you are losing to your competitors - So you can rake that lost revenue back in and become the best of the best, obviously. In short, social media is a cheap and low-maintenance way to increase your inbound marketing in partnership with your website. Get on it.