The assembly Mirror Components command can perform two types of mirroring operations. The "Mirror" setting creates mirrored part files, useful for making left/right handed versions of parts. The "Reuse" option creates an instance of the original part, located symmetrically about the mirror plane.
Currently the default option is Mirror. This causes my users (especially newer ones coming over from AutoCAD) to inadvertantly create a LOT of unnecessary part files when using this command. The vast majority of the time, Reuse is actually the option we need.
While this is largely a training issue, it would help a lot with accidental misuse of the command if there were an application option that allowed changing which mirror type is the default.