Tracking to discover latency, errors, weird behaviour, malicious actors and so on.

Tracking to see what content does well and what not.

Tracking to see what rough demographics (mobile, desktop, country, region, time-of-day etc) visit your premises.

E.g. plausible-analytics or even Matomo do a good job at i) keeping the data rough and broad and without any PII, and ii) storing the data on-premise rather than at commercial aggregators who will either re-sell or use it for own services.