Why Do Guys Catergorize Girls?

Yesterday, while talking to a friend that is a guy, he mentioned to me about how he "catergorizes" girls. My first thought of hearing this is that do guys think we are just numbers, or things, rather than humans? My second is why do they do it in the first place, to prove a point to their friends? That they can get a better girl than their buddies do? Or maybe that they are intamidated by certain type of girls, so they type them, by ones that I can talk to and ones that they can not talk to. I dont know the answer to all this, it just felt good to vent. Oh, and hi, internet.