What I mean by it cuts down on the total amount of variables to try and check against my keys script is that I only have vanitygen generating keys that are between 121-19z and 1A1-1Pz, It is generating more keys than that but those are the only keys being output to text file. By doing that I am reducing the number of keys I am checking against my balance list (which contains only addresses between those prefixes with a balance greater than 0).

I took all of the addresses that had a balance greater than 0 and sorted them by prefix and generated the graph below. As you can see vertical axis is the total amount of addresses that begin with each prefix (horizontal axis).