If you simply add JavaScript for analytics to your website, you’ll get basic traffic metrics, some fundamental behavioral data (such as bounce rates) and Top-N reports that show you the most common landing pages, exit pages, and traffic sources.

By adding goals to your analytics system, you can start to sort traffic according to business outcomes. Your top-N reports will now be about goal attainment, rather than being simply about popularity. You’ll not only know who’s sending you visitors, but who’s sending you the right ones. You’ll also know the most common paths through your site and where people are leaving.

By creating custom segments and tags that add context, you’ll know more about what’s happening on the site. You can segment traffic and understand which products, offers, or users behave in ways you want, and which don’t. This focuses your marketing efforts, site design, advertising, and keywords selection.

Using clients with custom event monitoring, you can see how visitors interact with your site. This isn’t for the faint of heart—it requires modifications to JavaScript and a lot more testing. You can also automate multivariate testing (or buy analytics tools that automate it for you), so you’re constantly testing competing layouts, offers, campaigns, and content. While this is a lot of work, the result is a site that’s constantly and automatically adapting to what its visitors want.