This may seem like a dumb question to ask on a blog, but I see it come up from time to time. I thought the case was settled, but apparently not. So I asked a writer's group for the cons and pros of a writer's website.
Three cons seem to be cost, time, and learning. While it's possible to spend several hundred dollars to have a website designed, it's not necessary. Using the free tools available on Blogger, my wife and I (neither of us designers or particularly computer savvy) designed and created this site for the cost of a couple of hours of intense concentration and no cash.
Time is an issue. To be effective, a blog, website, Facebook page, Twitter account, and more and more require attention and fresh—you will excuse the word—content. A someone pointed out, a blog or website that has not been updated for six months is probably more harmful than no blog at all.
Finally, you do have to learn how to use the computer and the blog tools effectively, but once you're up and running, it should be no harder than writing a letter.
The pros are more obvious. A website/blog is a way to build an audience while you are writing your next book. It is a way to raise your hand when someone is looking for information, which is why the labels (or keywords) are so important. It's a way share your thoughts about—and around—a topic that's important to you.
And it might actually engage someone enough to consider, look into, buy, read, and recommend your book to someone else.