Have you ever brought up a website on your phone? If you have internet access on your phone, you have. The U.S. statistic is about 20% of all visits to a website come from a mobile device. This statistic includes both phones and tablets (like the iPad). Now, have you ever been to a website that is packed with so much information and tiny links that you have to zoom in just to read what a company has to offer? And the links? If you have fingers bigger around than a pencil, forget about it. I will personally go to another site rather than fiddle around with those tiny buttons.
The primary function of a mobile website is to put all of your contact information up front, in a design that is friendly to smaller screens (and people with fingers bigger than a pencil). You could use your mobile site as a landing page for mobile devices, a page that mobile friendly and has your contact information (address, phone number, email, etc.) and a link to your full site or you can create an entire multi-page site. It's really up to you. However you use a mobile website, if you have a lot of copy on your home page, I would recommend having one.
"But bald man, only 20% of my visitors are using a mobile device to access my site? That's less than a quarter of my customers! I can't afford to have a mobile website built for 20%!" Well, while as a business owner myself, I can certainly understand the concern, I will put this another way: what if your business dropped 20%? What if 20% less customers started showing up at your brick-and-mortar store? Or, if you don't actually own the business, what if your paycheck was cut by 20%? I imagine you would be searching for another job in short order. While I am not saying that every website out there needs to have a mobile site, I have seen plenty that should have one. Those are websites that have a high bounce ratio (when someone visits your site and leaves without looking around at other pages...maybe because of normal-sized fingers?). If you check your analytics, an average bounce ratio is 60-70%. If yours are higher, you might want to research why that number is so high. I'm not saying it's because you need a mobile site, but it's something to think about.
And one other thing, did you know that the average width of an adult fingertip is 2 cm?
Have a great day, and remember to keep moving forward!