To me Google's Analytics is as important as indexing your site with Webmasters tools. Analytics provides statistical data about your site so you can keep very close tabs on axactly how your site or blog is performing on a day to day, week to week, month to month or even year to year basis.

The kind of data provided is vast and can be broken up into very small groups of information, you'll get info on your visitors, how many there have been, how many new ones vs old ones, how many return visits, etc, you'll also get info on exactly where in the world your site is being accessed from helping you make informed decisions about your content or target market, for example, you'll exactly how visitors got to your site, be it direct traffic, referral links from sites where your ads appear, search engines, etc.

There is such a wealth of information provided by Google Analytics it would be just a waste of time to try to cover any more of them, use it for yourself and tailor the benefits specifically to your personal needs. Signing up with Analytics is also free as are webmasters tools so there's no reason not to take advantage of it.