Jeff Greenfield shows how to prove marketing impact in a cookieless, privacy-first world by focusing on reach, not just clicks. With iOS and Firefox limits plus channels like CTV, podcasts, and digital out-of-home, cookies no longer represent real behavior. He says GA4 last-click views miss long lags, so track impressions and watch how awareness later lifts traffic, leads, and sales. Start by adding the impressions column to last year's daily spend sheet and correlating spikes to later results. For brands spending $10M+ across 3+ channels, Provalytics models omni-channel halo effects and time to conversion down to campaign, ad group, and creative. His test method is to cut over-invested paid search for a month, confirm conversions hold, then shift dollars into higher-performing channels like Meta. The takeaway: measure the eyeballs you buy, change one lever at a time, and forecast where the next dollar truly drives profit.