Full Answer
GA4 was designed for dashboard reporting, not raw data analysis. Its key constraints: sampling kicks in for large data sets, the default retention limit is 14 months (2 months for free plans), and you cannot join GA4 data with external sources like email lists or CRM records natively. BigQuery removes all three: permanent retention, zero sampling, and full SQL joins across data sources. Practical examples: query every session that viewed a product but didn't purchase, broken down by traffic source and device type, joined with your Facebook ad spend to calculate true ROAS at the campaign level. You can also feed BigQuery directly into Google's Vertex AI for predictive modeling, or connect to Looker Studio for fully custom dashboards. The practical gap: GA4 shows what happened. BigQuery lets you analyze why it happened — and model what will happen next.