ports ports and more ports.

I've been looking at a lot of the ports in the services file as well as what
nmap finds when I do some port scans and I'm not sure what some of the ports
that are opened do or if they need to be opened for network activity at all.
In other words if I disable them will my system stop functioning?

111    sunrpc
113    auth
513    login
514    shell
515    lpd

I pretty much get the meaning of what each one is from the name except
sunrpc. Do they need to have an open port for someone to function on a
local host though? Are there any serious ramifications if I disabled them?

Don