Main Blog and Secondary Blog

Hi,

I have a simple question and need an advice on this. I have read that I can do some changes in my blog settings to make my blog a portal-like solution. I have a good description for how to set a static page and a blog in my menu. But I have some thoughts around this: Is it recommended to have one blog instance for my main site (portal with static page) and another instance for my blog… like this structure:

http://www.mainsite.com (which is a static page in WP)
http://www.mainsite.com/blog (which is a new instance)

…or is it better to set everything up in one instance? Of course I know two instances will occupy more space on my host provider, but I want to know the best advice from you experts on this 🙂