In practice
Define the handful of events that represent real business outcomes before adding anything else; an untidy event list is worse than none.
Check it against a second source — the CRM, the payment provider — at least quarterly. Analytics drifts, silently.
Why it matters
It is the shared language between marketing, product and finance about what happened.
Consent, ad blockers and cookie limits now mean it undercounts, so knowing the gap is part of using it honestly.