Hi,
At around 09:00 Clamps on Math and Map Range nodes are ticked and this seems to make the grunge effect look most natural. Is this the only way to do that?
The clamp on the math node is pretty important, so that we don't accidentally end up with a value greater than 1. Using that in the subtract node could result in a value of less that 0, and in most cases neither looks great. The clamp on the map range node also helps make sure that the value doesn't go above the To Maximum. It's limiting the dynamic range and removing detail, but in a way that's helpful here. You could try to adjust all the values manually to be between 0 and 1, but it's much more of a hassle. Hope that helps!