The idea is to make a mask for the pebbles. Please explain why the map range node is chosen, valued at 10, and plugged into the factor to accomplish this.
Hi Eric,
Like you say, it's a choice. The Output of the Color Ramp doesn't reach 1, because the white was changed into a grey. For a Mask you want black and white Values (and often not much in between). An alternative to the Color Ramp in this case, would be a Math Node set to Multiply by 10. This would do the exact same thing.
The Values then are between 0 and something around 9 or so, but the Mix Shader Clamps its Input (Factor) between 0 and 1.
Yeah as Martin says, there are so many ways to accomplish the same thing, the way you go about it comes down to personal preference. If your like many of us and consider the Map Range node to be a creation of Satan himself, trying to get my head around it I once asked JL if he could go deeper into how it works and he made a video for it. I'll leave the link if you're interested and haven't already seen it:
https://cgcookie.com/lessons/bonus-understanding-the-map-range-node