A useful marketing dashboard has few enough numbers that someone can scan it in thirty seconds and know if the business is on track: pipeline or revenue generated, cost per qualified lead or CAC, conversion rate at the key funnel stage, and your north-star metric. It should not be a wall of every metric each channel tool happens to export — impressions, likes, and raw traffic without context are noise dressed up as data.
If a number on the dashboard has never once changed a decision, it doesn't belong there. Most teams over-build dashboards early and only trim them down after months of nobody actually looking at half the tiles.