In The Search, Federated Media author John Battelle writes that search engines have revolutionized marketing by capturing a potential buyer at the moment of their intent. A user tells the search box what she wants when she wants it. Unlike contextual advertising, where you may buy an ad on Oprah if you want to target ladies and very sensitive men of a particular demographic who may (or may not) be interested in your offer, with SEM you don’t have to guess at who is looking for your product.
With the correct approach, you can tap directly into the stream of millions of queries related to what you are offering that are being typed by qualified buyers as you read this. Capturing them at the moment of their intent at the very least requires your presence in the marketplace. If you do not have your site listed on the first three pages of google search results or a Pay Per Click ad running with a compelling offer when that user comes searching for you, someone else will get their business.
You have to show up to compete.