Why do a Blogger blog? Or host one on Wordpress?
Simple - to get traffic and better rankings for your main hub. Now, Charles Heflin and others refer to these as "junk" blogs. Because while they can get you some affiliate income, they aren't your main line of business.
And after years of blogging (and a few paltry affiliate commissions during that time) I've been prone to agree.
But I'd take this further. Blogs are not your main line of work, either.
The blog is not the product.
Sure, you have some fun with these, and blow off steam. And you can be as educational as you want. And blogs aren't your main hub, either.
Your hub is where the action is. Opt-in lists are part of that - but are the auxiliary part. The idea is that you provide a valuable service or product and make it available online - or give someone a contact point where they ask for someone to contact them.
Blogs are meant to be informative, entertaining, even enlightening. They don't produce direct sales. They simply encourage action - whether it's to follow up a link or opt-in to a mailing list.
The key point is to fine-tune your hub to ensure it gets optimal conversion.
And fine-tune your blog posts so that they give a relevance to your hub.
Why should they be two separate lines?
Well, you can have them both on the same spot. Just make your main page a static one, and the articles show up under their own category. Problem is (and this is my difference with Wordpress as a do-it-all wonder platform) things can get clunky over time. I've been kicked off (and nearly so, as well) from internet providers as the plug-in conflicts took up too much bandwidth and tied up servers.
This is why you should let someone else host your blog and take care of the back end. You then can concentrate on having a real, dedicated, SEO-driven CMS for your central hub.
The point is to have your hub rank routinely on the SERPs while your hub is popular in the social networks (and might show up on the SERPs as well - a bonus).
Your blog is an entry point to the dining room - but your hub is the main course and dessert.