It's not necessary, unless you want to get traffic from search engines. If you have some friends that you are blogging for, or another way of contacting and inviting the people you want to read your blog, there's no need for seo. But if you want to attract new traffic to come in to your blog through search engines, your going to want to make sure your site is set up as well as possible for those engines to index and rank your site well.
it help to get traffic on your internal pages (posts), people type long tail keywords, and your blog post can be appear in google, yahoo etc..
SEO = Targetted Traffic If you want to make money from blog by PPC ads like adsense, you want people who are willing to click on them who are interested in them. If adsense places ads depeding on your content then it is obvious it will be the same people clicking the ads who are visiting your blog because of an interesting post or something. So, if you want to make money you need targetted traffic and SEO brings you targetted traffic.
If you want to make tons of money online, SEO for blogging would be your guide on making it possible. It will bring quality traffic that may lead to earnings.
SEO is required because doesn't matter how good you are at blogging, people should find you. SEO is one part of the website promotion story, you need people to come to your blog first (using promotion) and if you are good they will come again.
seo is not necessary for blog but some time u get good traffic to blog you promote your blog on good way so you get good traffics, good PR blog is one type of free small website
If you want to earn or want to make famous your blog on internet, or need good amount of traffic at your blog so according what ever i hear and read till not seo is require.