A dashboard with forty charts is a place people go to feel informed. A dashboard with six is a place they go to decide something.
A car dashboard, not an aircraft cockpit. Six things you glance at while driving, not four hundred you consult on the ground.
A dashboard serving three audiences serves none, and the abandoned ones cost refresh spend forever.
A dashboard is a monitoring instrument, not a report and not an exploration tool. Its job is to let someone see, in a few seconds, whether anything needs attention — which means a small number of metrics, each with a comparison so the number has meaning, arranged so the most important sits top-left where the eye lands first. The commonest failure is scope: a dashboard asked to serve executives, product managers and analysts at once serves none of them, because those three need different aggregation levels and different refresh rates.
Design for one audience and one decision. Five to seven metrics maximum, the most important top-left, every number carrying a comparison (versus last period or versus target), filters that persist, and an explicit as-of timestamp. Detail lives one click away, not on the same screen. If nobody can name the decision it supports, it is a report.
Data Dashboard Design Best Practices — OneNumber - Tableau Experts, 9:58