What's the benefit of working in this particular way?
Decals are one of those things that I always wanted to explore, so I thought it was pretty cool to see this video pop up in the feed. I'm not really sure what to make of this workflow though. As far as I'm aware, everything that this method does can be done just as well using the shrinkwrap modifier. It's true that you need to add a decent number of subdivision to your image plane, but booleaning out parts of your current mesh can also result in any number of vertices.
If your mesh consists of multiple objects you can join them together (or duplicate them first and join them to use as a 'guide' object)
There's also always the option to add the decal in your material, combined with a UV project modifier so you can even combine elements of your base material with the decal
Maybe I'm missing something, but I don't fully understand what the idea behind actually booling + cleaning up your mesh is supposed to offer as an advantage. I was kind of hoping for a way to easily project decals over a variety of meshes / objects without having to add modifiers to every single one of them. I believe that UE4, for example, just allows you to easily project decals like this over anything in the environment. I kind of hoped Blender would have something like that now that EeVee's here. Would love to hear your thoughts! :D