In 0rder to take a little tour on the topic titled, "What is the purpose of building a nice blog?", let me first tell you what is a niche blog.
Any blog that deals with a specific topic is a niche blog. You can call it a specialty blog.
Niche blogs would given the status of niche blog if it contains about 100 blogs focusing on hundreds of sub niche keywords.
For example, if you have a blog exclusively on raising an organic flower garden, you would have so much to write about that would fill hundreds of pages of your blog.
Finding long tail keywords and sub niche keywords:
For filling up your blog with 100 posts on your basic niche which is organic flower garden
you have to find roughly 1000 related keywords and long tail keywords using a couple of free keyword research tools.
Long Tail bird-Image via Wikipedia
What is the purpose of building a nice blog?
Of course definitely not as a hobby-niche blogs require too much involvement. Therefore, it is for earning money, people build and maintain niche blogs.
You can monetize your specialty blogs with lucrative affiliate links and Google ads. Both will fetch you a decent sum in the long run. So much so that you will think of building your second niche blog in exactly 12 months.
How much you can earn per niche blog?
I have written a blog post long back on how much you can earn per month from a single blog.