Question about using sub-domains

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.

By the way, I really like the idea of sub-domains and I'm exploiting its market potential in my websites. And I agree that there seems to be a scarcity of opinions on the matter. I suspect that the reason for this lack of opinions is that the sub-domain is really a simple feature and there's nothing miraculous nor technically exciting about it.

Anyway, here's what I know about sub-domains. A sub-domain is really nothing more than a sub-directory or folder in your site. So, weightloss.isgreat.com can usually be accessed as isgreate.com/weightloss.

There is also no added advantage in site management. In fact, it is an added step. And in terms of security, you cannot really secure your root without affecting the sub-directories or folders. Stating it in another way, you cannot really sell the sub-domain separately and give control to just that portion of your domain.

kanshu,

Thanks for the reply and your thoughts on the matter.

I am leaning heavily towards using sub-domains simply because I am just getting started in this, am unemployed, so money is an issue.

I understand the downside of not being able to sell something that is on a sub-domain; but, if what I have in mind actually works, I doubt I would want to sell anyway.

I do like the idea of being able to choose keyword related sites to send people to (weightloss.isgreat.com); but, I still wonder how the search engines view sub-domains.

Again, thanks and have a good evening.

In my experience, subdomais are almost as good as the domain itself when it comes to SE. Besides what Kanshu said, direct traffic is a problem. Noone will type weightloss.isgreat.com for instance.

Thanks for your input. I will consider what you said. Not sure what direction to take yet; but, I'll figure it out.

Have a great day!!