Google Adwords Keyword Tool is actually meant for advertiser that want to advertise with Google. Using this this keyword tool, advertiser could get valuable information about keyword that that want to advertise.

Using Google Adwords Keyword, advertiser could know :

the estimated number of search for the keyword
the estimated number of local search of the keyword
the price of the keyword per click
the number of current advertisers for the keyword

Since Google Adwords Keyword Tool supplies a lot of valuable information, most blogger use this tool to do keyword research for their blog post.