Speaking as s very inexperienced collector, grading does influence my purchase quite a lot with some coins.
For example, I picked up an 1852 $1 gold AU55. For that type of coin the pricing was reasonable, but I hesitate to drop much over $100 unless I'm certain it's a legit coin and the grading is right. Professionally graded coins make it easier for me to be comfortable with those purchases.
I also bought a graded 1943d
Mercury dime. It was my first time in that shop, and the owner had let me pick his brains for a bit, so I wanted to buy SOMETHING, just to establish myself as a customer. I figured the $10 he was asking was fair for the dime, and I was curious why someone would have a dime like that graded. I might have bought a different coin if not for that.