I didn't say it was the entire score (unless all you have is a credit card).
You can call up the agencies yourself and ask. They will tell you that the optimum is something like ~30% credit utilization. More or less than that will affect your score negatively.
I imagine how big/small that affect is depends on all sorts of other factors.
Edit: It's stupid. Shortly after college, when I had to start paying back student loans, I decided I wanted to try to "build credit," so I got one of the few cards they were willing to give me. My (already not great) credit score immediately dropped.
When I looked into why, I learned about "credit utilization" and why you always want to carry a balance if you want to build your credit.
It's fucking stupid.