You see that 35 people from the US viewed the page during the selected dates. 4 of them viewed a saved run and 31 started a new run. 20 of those 31 paused it to hit clear or save, I did not extend the image past that, but you would be able to see how many people eventually saved their run (not the actual run and the data associated just the event of saving it). Out the 11 that did not pause 3 had errors. Without event tracking I would have only seen 35 visits from the US and missed out on all this other data.
Tracking errors with events is a great way to see what is happening out in the wild. As we saw in the events flow report I had some errors come up. In my error handler for GPS I track the category as Error and the action as the error code. The error codes match what is returned from the location object according to the API. The three values map to 1= PERMISSION_DENIED, 2 = POSITION_UNAVAILABLE, and 3 = TIMEOUT. I can view my Error category and get a rundown of all the errors on my page.
This report shows I had 12 events where permission was not given to track the location and 4 timeouts. The other event is the clear modal after the error. You could have client side issues and errors and most people will not send a bug report back to you. With event tracking of errors you can see exactly how many errors and hopefully why. You can also tie in other information like browser and OS version to see if you have a specific bug that only affects a subset of users.
Unobtrusive Event Tracking
I found a great jQuery plugin to do Google Event tracking. Because it is jQuery you don’t have to worry about cross browser issues. It allows you to easily add event tracking to an existing page or to on a new page. It attaches right to the click event handler so you don’t have to muddy up your HTML with a lot of onclick attributes. It has the ability to use HTML5 data-* attributes to set category, action, label, and value. It has many options that should be able to suit your needs. It is also hosted on GitHub.