The --remove-short-arcs option is no longer needed
In the past you would get many "zero length arc" errors.
SEVERE (RoadNetwork): 63240020.osm.gz: Road (...) contains zero length arc ...
These were not caused by bad map data, or something that you could do anything about. The solution was to give the --remove-short-arcs option. If you did not give that option, then you could get routing errors in addition to those error messages. This meant that the option was effectively required.
This has now been fixed and in the latest versions of mkgmap the option is no longer required and at some point in the future it will be removed altogether.