Main benefit with this approach of G-code generation is the control over every vector of your G-code.
With conventional slicers you are left with planar cross-sections of the 3D mesh and can't control the extrusion path itself.
With fullcontroll.xyz you can edit every point and its properties like speed, extrusion values or non-planar coords.
I've been developing a similar add-on for Blender called nozzleboss. https://github.com/Heinz-Loepmeier/nozzleboss
It lets you use Blenders modeling tools to create toolpaths directly and export to G-code.
It has an importer as well, that lets you edit existing G-code with Blender,
e.g. using sculpt tools to deform G-code paths.
https://www.youtube.com/watch?v=aoM8-Xdh9w8
Using Blender is nice here, because you have access to so much modeling tools already
and don't need to code to generate G-code (though you could, Blenders python api or geometry nodes is very well suited for that).
The add-on uses vertex colors to store meta information on every segment of the G-code,
so you can paint on extrusion/speed multipliers or color itself very intuitively.
(Different colors in FDM printing are usually done by segmentation of the mesh into different parts, which can be difficult.
Though PrusaSlicer introduced multi-material painting recently, so if you are interested check that out.)