This methods are based on "converting" a surface definition from explicit to implicit and vice versa.
For example, I begin from explicit (usual polygonal) surface and measure a signed distance to it from an arbitrary point. Then, I perform some computations (like boolean, blending, etc). Finally, I take a new polygonal surface, that is smooth and topologically equivalent to my implicit result and iteratively push down it's points to zero level (by gradient multiplied by SDF).