A very common thing that I setup tracking for on a variety of pages for different companies is how their main menu is used across the site. The main menu is usually where most of your visitors will look at if the page they landed on didn’t really hit the mark. That’s if you’re lucky, otherwise they’ll just hit the back button at go back to what ever Google search that led them to you in the first place.
Sites usually invest some thought in the navigation and by that it’s of course important to measure how your site’s visitors will use it. In Google Analytics you can of course see how many of your visitors that looked at, say your Product Overview page. You can also see how many of them that came from, say the start page or a specific product page. But you can’t really see how many that used your sites navigation in order to from one page to another.
Luckily, you can set up tracking on that using Google Tag Manager in basically a few minutes.