How do things like cleanupIdleSessions interplay with database/sql's connection pooling

[budden]

This question arised from learning this one:

http://go-database-sql.org/connection-pool.html

I did neither careful code study nor experiments, but there is a feeling that there's no need for files like pkg/api/session_cleanup.go. Instead it should be sufficient to configure an sql's connection pool feature. Am I wrong?