You might not have been using it correctly, for me the resulting .clean file is on average about 2-5% smaller. It seems to remove movements that are 0.01-0.05 units difference, for example, in the KISSlicer output there are these two lines:
G1 X80.68 Y127.83 E9.0086
G1 X80.64 Y127.81 E9.0097
and the script will remove the G1 X80.68 Y127.83 E9.0086 as its only X0.04 Y0.02 units different. I've been using the script for about year now and it hasn't had any ill effect on the print so I believe it's helping to reduce unnecessary movement and reduce gcode filesize.
I was hoping lonesock would have implemented some of these efficiencies in KISSlicer since then. I will keep using the script until I hear otherwise.
thanks