When you or I have a problem, it’s pretty easy for us to imagine a solution. And that solution is filtered through our experiences and responsibilities.
Designers don’t just like to design, sometimes they like to read. But there are many design articles on the web that go unread because of the lack of exposure.
Imagine being able to see what area of your site users interact with the most. Wouldn't this make your job easier? That's what heatmaps allow designers to see.
There comes a time when a designer is done wireframing and needs to focus on the style of their site. But without the right graphics, this is hard to do.