Yes, SEO professionals need to keep up with Web traffic on competitor sites, but knowing the tools to use can become challenging, especially when there's so many from which to choose. Sam Crocker
provides a list of resources that many can add to their tool chest, serving up descriptions and strengths and weaknesses of each
Read the whole story at SEOmozBlog »
And why do professional SEOs need to know how much traffic a competitor's site is getting? Perhaps to gauge how well their techniques are working, since it would be rude to ask them. But I really have little or no interest in knowing such things.
My site or those of my clients are the sole focus of traffic concerns. Even the author of the article ends with a vauge, "...I'm sure I will come up with some creative ways to use these insights."