For most people, none whatsoever, you can team ports together but that requires support from a smart switch the other end. You usually do this on servers or its a feature of some NAS boxes.
The other option is to give your PC two IP's using a dedicated port for each of them, perhaps for a VM you are hosting or a particular application/service whose bandwidth requirement might interfere with whatever is happening on the other.
Some people for instance might run an entirely separate network (switches, cables the lot) for their backup or Media streaming setup to keep it away from other traffic.