This entry to Paścimatānāsana helps the spine's elasticity before entering longer holds in the posture as either a mudra or further vinyasas.
Supported (salamba) Paścimatānāsana vinyasas to bring ease in the posterior chain and ease the flow of prana in the central channel
This video shows the counterpose for paścimatānāsana: pūrvatānāsana (the anterior stretch pose)