[mytailorisrich]

What is the business justification for creating a blog on your website?

In general I would think that it is to create contents and SEO, in which case I believe that it is better to host it under the website's domain. On the other hand you may be targeting a different audience from your main site/product. For example Uber, Netflix at al have "engineering blogs" these days, which clearly have no relation to their product but perhaps rather aimed at being a recruitment tool. In such case you might want to use different domains (which incidentally is what both Uber and Netflix do).

I see people commenting on the technical aspects but the differences are minor and the business goals should be driving the decision.