A lot of ShaderToy demos share the Ray Marching algorithm to render the scene, but they are often written with a very compact style and i can't find any straightforward examples or explanation.
So what is Ray Marching? Some comments suggests that it is a variation of Sphere Tracing. What are the computational advantages of a such approach?
How do you write a raymarching shader?

Ray marching is a ray tracing variant that approximate intersection points using iterative steps instead of a lookup table. This method is computationally cheaper than exact ray tracing because it doesn't store pre-computed collision results for every object as ray tracing does. Each ray is marched iteratively towards the intersection point, and the process stops when the ray intersects a geometry or reaches a maximum iterations limit.
In which use cases should i consider ray marching?
Thank you for any links to resources.
A common misconception about ray marching and sphere tracing (as far as I can tell) is that they are the same technique. They are actually quite different, although there are similarities.
Ray marching is a simple and relatively fast technique for rendering volumetric scenes, mainly inspired by ray casting and ray tracing but with some important differences.
The core idea of ray march