Since Compass is an analytics dashboard, we use Google Analytics information for many of our metrics, e.g. the number of people visiting your site as well as a breakdown by acquisition channels (e.g. organic, direct or referral traffic). Since these metrics are an essential part of our product, we have made it compulsory to connect Google Analytics.
If you don't have Google Analytics (GA) yet, there are many reasons why you should set it up, irrespective of Compass. This FAQ article explains how you can get Google Analytics for your website.