Every writer should have a platform. There are many ways to establish a platform, including writing books. I've spent the last 16 years building my platform and presence online. Having a platform, especially a large one, is something agents, publishers, and even television producers consider when deciding on taking a chance on you. A compelling product (book) is great, but it doesn't do you any good if you don't have the "eyeballs" out there to market to.
In March of 1999 I opened up my photography forum--way before there were social media channels. Facebook, Twitter, Instagram, Pinterest, LinkedIn, etc., didn't exist. My forum took off, I then landed a book deal with a publisher of photography books and wrote four for them before I went self-published. Somewhere in there Myspace became a big hit, then it became a big bomb. Things change every Monday when the Board of Directors Meet--you have to evolve with the times by staying informed. As they say, the train will leave you behind if you don't get on board.
My experience, my forum as did that of many other forum owners had a great run, but soon because of my genre, photography, was replaced by social media--so I jumped on board the social media train. When the forum traffic decreased, I had to adjust and opened up my social media accounts as well as started a blog, then another blog.
Just like people use different modes of travel to get from point A to point B, i.e., trains, planes, automobiles, etc., you have to use different modes of building your platform. This includes maintaining an email list, participating on the forums like this one that are still out there, a blog, and social media engagement. My recipe is Twitter, Facebook (fan page and personal accounts), Instagram, Tumblr, blogs and participation on genre specific sites. Does this take time during the day, yes it does and you have to allocate that time in order for it to work. Doing nothing brings you nothing. It's about working hard and playing later.
Take away technology from the past 20 years, take away Amazon, Barnes, iBooks, etc., and how many books would there really be out there today? Probably millions less than today because technology today has changed the publication landscape in a manner where every Tom, Dick and Harry is writing books, blogs, articles, etc., and it's an oversaturated market, with many non-professionally edited books, that you have to wade through to really find the masterpieces. That said, what created this mess is what you have to use to get seen and to sell your books. That's my two centavos worth!