What are parameters used for?

Parameters are user-supplied values — number, text, date or a list — that can be exposed as a control and referenced inside calculated fields.

Typical uses are metric switching with a CASE expression, threshold inputs such as a target line, and passing a value into a BigQuery custom query.

They are the main route to interactivity beyond ordinary filter controls, because a filter restricts rows while a parameter can change what a calculation does.