Joe, Actually "use default if unwired" has nothing to do with any "default case" and does not require the presence of a default case. It simply assigns the default value for the given data type to the output tunnel in cases where it is not wired. (examples: a DBL gets 0, a boolean gets "false", a string gets "empty string", ...).
Kura, Are you are building an array in a loop coming from a shift register? In this case you would wire the existing array across so nothing is added unless the other case is selected. If you leave it unwired and set to "use default if unwired", your entire array would be replaced by an empty array. If I did not understand your problem correctly, please clarify and maybe show a small example.
