Let's say you're considering starting a new website, or venturing into a new product niche. And, suppose you'd like to somehow determine how much search buzz is currently hovering around this topic. You can use Keyword Researcher to get a "feel" for how much interest is actually out there. For example, let's say you were selling cameras. Then you might consider the following:
If you're struggling to think of more keywords people might be searching about a specific topic, go to Google.com and take a look at the related search terms that appear when you plug in a keyword. When you type in your phrase and scroll to the bottom of Google's results, you'll notice some suggestions for searches related to your original input. These keywords can spark ideas for other keywords you may want to take into consideration.

Long Tail Pro is a keyword research tool that helps you quickly find low competition keywords for your website.  In particular, the tool is built for people doing SEO (search engine optimization) as opposed to people doing paid ads (Google Adwords PPC).  I'm sure there are some advertisers that use the tool for paid ad keyword research, but the tool was built for SEO keyword research.