Does it matter? As for me, protection is required to either side.
Of course it matters, but in the case if it is required only for one side.
What do you mean. Both the client and the server have to exchange information in order to stay up to date.
Let's say someone takes the coin you caught 2 minutes ago. How would the server know you caught that coin, if the connection is one-sided. Or, how would you tell the server that you caught it.