Right, but you won't know much about your users if you don't. What if you ran an arbitrage site for 3 months, no tracking. Then you started tracking and realized you had a bounce rate of 50%. That's half of your ad budget... You can use that information to dig deeper and figure out whats going on and where you can improve. So, essentially that would have been 3 months of un-optimized traffic.
There are tons of little things that you can analyze to more effeciently influence the users decision on your site. In this case, increased CTRs on ads. Without tracking those metrics, you can't really do much.