The board provides flyback diodes (freewheeling diodes) for the motor outputs, so that they are also protected against induction voltages in the unpowered state of the driver.
You will get smoother movement especially on the delta-style 3Dprinter under DVR8825 stepper driver and A4988/ 2 drivers.
Lower vbration lower noise smoother result!

Package includes :-
2 x TL Smoother with connecting wires