Gauge wire for Jabsco pump?

I have a jabsco ballast puppy I just purchased for my ballast system. I have 14ga wire running to right where the pump will be. Don't know why its there, but it's awfully convenient. Hopefully it's all hooked up under the dash. Anyway the wire is 14ga and also the leads coming off the Jabsco are 14 as well. Seem like a good match. However I've seen people recommending thicker wire. I am not sure what that would do since the jabsco has 14 on it already and I'd like to avoid taking apart and rewiring my brand new pump. I haven't measured but based on the distance I am running the wires I think i am right in between needing a 14 or 12ga. But if the leads on the pump are 14 how would thicker wire elsewhere help?

What is my misunderstanding here or what other comments do you have? What about fuse size?

Thanks in advance