It will be useful to have key mapping to make some mapping depending on the connection. For example, in some system "delete key" did not work, only work "backspace key", so "delete key" should be mapped to "backspace key". But if we have a connection to other system where backspace and delete are valid keys, it win't be necesary to map. So the mapping should be per session.
And example of that exist in putty software, under Termnal group of options, exist the option "Keyboard". Another example can be fouund on propertary software of VanDyke "SecureCRT".