Subdomain questions

If I was to build a site that was (mostly) white hat, what would be the disadvantages of having several (perhaps 200ish) sub-domains on a single domain?

I am also interested in any info regarding subdomain blogs. I've read somewhere on here that the max you should host is 6-8, but I can't find the exact post at the moment. Does anyone know why?

a sub domain is a standalone site under your main site. you will have to promote it in search engines from scratch as it was a different site.

The advantage is that you can create a sub domain for each niche and by that focus your keywords instead of spreading them in your main domain.