It depends if you run the full node with open port 8333 to allow incoming connections or not.
Good point and most home users (Not miners) would not know how to port forward the router so I let nodes connect to a program that
I am working on and then reverse the direction and keep the connection open so that they become useful and not just parasites to the network
The upload volume is high compared to the download volume. It is at about 17 GB per day.
These numbers are not bad and you can use QoS in some routers to limit the traffic if you needed too
but on larger systems (100m nodes) network chatter really does become a killer without a degree of
centralization but few people here are prepared to accept this conclusion that "free for all" has it's limitations.