A scale helps, especially when you're new to keeping snakes. Underfeeding is a major issue in this hobby. Do you have to have scale to successfully keep a ball python? No. Do I rely on mine 100% and weigh every meal? Nope, but it helps sometimes and those new to keeping them might not know exactly how big of a meal is best and a scale helps teach them. People also like to keep track of their snake's growth.
I'll bet the majority of underfeeding issues are due to "Bob" at Petco telling the new snake customer "just give 'em a mouse every couple of weeks and it will be fine. They're snakes, they can go months without eating..."
That or laziness or cheapness...
Lucifer Sam, Siam cat...
Always sitting by your side,
Always by your side...
That cat's something I can't explain...