What is the primary operational purpose of the Minimum Vectoring Altitude (MVA) established for radar controllers in the Approach Control Unit?

1. To determine the maximum cruising speed of jet aircraft in the circuit
2. To dictate the minimum altitude at which cabin depressurization drills may occur
3. To indicate the lowest altitude at which a VFR flight may operate without a radio
4. To specify the lowest altitude at which a controller may vector an IFR flight, guaranteeing required obstacle clearance