Hey Dave Z...I think of the brick or post war ZW as a big hammer waiting to clobber the tiu with excessive power in the event of a short on the layout. With the fuse between the power supply & tiu the power surge is going to be stopped before it has a chance to flow through the tiu.
I suppose the track signal might not be as good if it has to flow through the tiny fuse wire if the fuse was installed track side of the tiu?
Which would blow first??? good question.