Controls if pre-contact and pre-continuous callbacks will be called. This only applies to Dynamic bodies and is ignored for triggers. These are relatively expensive so disabling them can provide a significant performance benefit.
A shape only produces these callbacks if its own PhysicsShape.preContactCallbacks is also set. The deprecated Unity.U2D.Physics.PhysicsCallbacks.IPreSolveCallback is also driven by this switch, for targets that only implement it.