If your most common keywords are not a proper subset for your niche or target audience you're likely missing out on some traffic.
For a long time in search engine development the exact matching of keywords was the target, thus the rise of keyword rich domains, the placement of specific keywords in title, description, text, page names, alt tags, et al. That was something that SEO offered to the average person who had no clue about what elements of page design would be most effective.
During that time period I studied my GWT keywords religiously.
My attitude has somewhat changed now in the Age of Panda because Google set out to kill SEO and (to my eyes) succeeded. Now, I believe they use advanced algorithm design that is almost akin to AI to determine the overall focus of a website, then attempt to match the most "trusted" sites within that focus to a query. So if you're doing a generalized search for something like "widget wonders", it is less important than ever for that specific phrase to be on a page because Panda is making a determination based on hundreds of other factors.
I hasten to add: That is not always the case however, especially when looking for something like an owners manual for a specific product model (Query: "WidgetWonder 123.456"). In that example, there will likely be a more exact keyword match (if possible).
So like everything involving Panda, there is no universal rule. It depends on the specific query, the Panda
interpretation of that query, the Panda
evaluation of existing sites within that niche, the user behavior history, et al.
All of which is just a long way of saying that I use GWT only occasionally these days because nothing makes sense to me with Panda. I can find no clues that lead to any universally accurate conclusions. That is true whether we are speaking about keywords or backlinks or site speed or website age or original content or anything else ~ Panda sees everything through its own prism, and the contradictions are everywhere, so in my mind at least, that prism is unknown and unknowable.
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