On a small day-sailor or dinghy, what is the primary hydrodynamic function of the 'Orza' (Centerboard / Daggerboard)?

1. To provide forward propulsion when there is no wind in the bay
2. To serve as a ladder for boarding from the water
3. To act as a trim tab to level the boat at high planing speeds
4. To generate lateral hydrodynamic resistance and prevent excessive sideways drift (leeway / deriva)