I like to explain in a simple way Google Webmaster Tools is a sweet suite of Google SEO tools that gives data and configuration control for your site in Google. If you're doing any SEO and you don't discover value in GWT. I'm using GWT for finding technical issues of the website.
It's good to use if you have a forum to constantly upload sitemaps. Xenforo supports automated sitemap uploads so that comes in handy. Ever 2-3 days a new sitemap is uploaded if there have been any changes. I also use it for monitoring keyword progress in Google.
To keep track of keywords and so forth that are being added by google. So far a few have been added but I'm hoping to get more content for my site so a lot more keywords are added in the future. Would help out a lot and I'm hoping it does better.