To build a successful blog you need to appear within the first 5-10 results on a Google page for whichever term your blog is officially about. Why? Just think of it this way: When you do a search how often do you actually go past those first few results?
SEO is important for a lot of reasons – the most obvious being so that your site or blog appears in a good place in search engines. But there are other reasons too. Your SEO affects things like your Google Pagerank, and most importantly the number of visitors you get.
If a tree falls in a forest and there is no-one there, does it still make a sound?
This can be applied to your blog: If your blog exists, and has content, yet no visitors, does its existence have a value?
Good SEO can put your blog at the top of Google, Bing and whichever search engine you want. It also means that when people visit your website they can find what they’re looking for, and other things they are/might be interested in with ease.
Bad SEO will get you blacklisted, ignored, forgotten. If someone finds your website they probably won’t stay long. It will probably be hard to navigate, not give them the information they want/need and do its absolute best to scare them away.
Even if you don’t want to make money blogging, become wildly successful, or really do anything more than just have a blog, it’s worth understanding why SEO is important, and the difference between good and bad – because if you ever want someone to find your blog, or the information you’re sharing, then SEO will make or break your chances.