The cardinality statistics for a table influence the optimizer's choice of a query plan for a query which accesses the table's data. If the cardinality statistics are missing or out of date, the optimizer may choose an inferior query plan, resulting in poor performance.
One common situation which can causing missing or out of date statistics is when indexes are created before the data is added to the tables. Cardinality statistics are automatically updated when an index is added to an existing non-empty table, but adding, updating, and deleting data after the index has been created can cause the cardinality statistics to go stale.
You can find additional information about these system procedures, including the syntax for invoking them, in the Java DB Reference Manual.