One problem. If your visitor fires off many events quickly, less than one second apart, then the order of those events may get lost. A second event may come in before the first.https://community.mixpanel.com/sending-data-to-mixpanel-11/order-of-events-3136
Ugh! Why do people use it? Because when it came out, it was free, and one of the best (there was not much competition). Can't beat free. Google is a trusted brand with great products, and a lot of marketing power. So, people trust it and use it, often exclusively. The problem is that it is very difficult to do anything custom in it. The features you get are not as good as some others like Mixpanel or the tools below. Actually, it is difficult to see what's going on on your website, except for very basic statistics.
seems to be the best dashboard, best breakdown of user interactions (I work atSpiral.us, they use Tableau. I see screenshots in meetings, looks powerful!). Unfortunately, it looks like it takes some effort to set up, and their free trial signup is broken. Will try again later.