The ability to create campaigns that can be tested and validated against KPIs easily via Google Analytics. It's easy to set up custom dashboards, as well as test different segments or scenarios within your tests. I wish there was an option to save multiple versions of my data so it would keep track of what changes were made between iterations. Also, having the reporting dashboard available at all times when testing new content or ideas. This tool allows me to quickly build out A/B tests without needing to wait days or weeks until I have enough traffic.