Google sunset Universal Analytics in July 2023 in favor of Google Analytics 4 (GA4), which shifted from session-based tracking to an event-based data model better suited to tracking users across both websites and apps. Two of the most important efficiency metrics in marketing are customer acquisition cost (CAC) -- total spend to acquire a customer -- and customer lifetime value (LTV) -- total expected revenue from that customer over time; a healthy business generally needs LTV to meaningfully exceed CAC, since a positive but thin margin leaves little room for operating costs. UTM parameters are tags added to a URL (such as utm_source and utm_campaign) that let analytics tools attribute a website visit, and ultimately a conversion, to the specific channel, campaign, or even individual ad that drove it -- without them, traffic from different efforts gets lumped together as generic 'referral' or 'direct' traffic. Making decisions from this data, rather than from opinion about which channel 'feels' like it's working, is what separates data-driven marketing from guesswork, but it requires the discipline to tag campaigns consistently before launching them, not after.