Newbie With a Question

Hello Black Hatters!!

I have been looking over this site for 4 months now reading information and gaining some ideas. I must say, some of you are very impressive and I hope to glean a lot from being here.

I have a question about sub-domains. I haven't really seen anybody touch on this, either positive or negative; so, I'm going to put it out there.

How does using a sub-domain affect how the search engines rank a site?

Let's say I have the domain name "isgreat.com" and I want to use it for niche sites and/or blogs. So, I create a sub-domain for a weight loss product and name it weightloss.isgreat.com and then I want a blog to review the weight loss product and I create weightloss.isgreat.com/blog

With such a domain name (isgreat.com), I could create unlimited keyword rich niche and/or blog sites.

What do the pros think?

Thank you all and have a great evening.

Okay, so, who am I? I am a 47 year old female who lives in Indy. I lost my job a little over 2 months ago (my highest paying job so far); and, just a few minutes ago, my favorite car of all time got repossessed.

I am scared to death at the thought that I am starting over at this point in my life; but, at least I have unemployment benefits for a few months.

So, any fast-acting advice and an answer to my original question about sub-domains would be greatly appreciated.

I hold on to the dream that I can get enough income going before my unemployment runs out and I hope to never have to punch someone else's time clock again.

Right now, I am so sad.