In practice
Look at adoption curves, abandoned steps, ignored features and workarounds built in spreadsheets. This is revealed preference: what customers need in practice, which may differ from what they said they wanted.
Behavior isn't the same as product analytics. Behavior is the signal layer. Analytics is one way to measure it.
Why it matters for product builders
Behavior includes the people who never write in. It's the only signal layer that covers the silent majority by default, and it helps you spot the gap between requests and real use.