Digital marketers should consider online data co-ops for three reasons: 1) First-party data alone lacks scale while third-party data can be costly and inaccurate. Data co-ops provide a scalable and validated alternative. 2) Data co-ops allow marketers to gain insights from aggregated first-party data from multiple brands and publishers, providing more reach and granularity than any single source. 3) Case studies found marketers who used a data co-op approach saw improved marketing ROI, customer acquisition, and customer experience versus relying solely on their own first-party data or third-party data.