The perfmon class spams stdout, this is not a big deal for GUI usage of Blender but makes CLI/automation use-cases difficult. We export many blend files to FBX as part of our pipeline and this makes our logs unreadable.
Example of output when exporting FBX file from Blender with PERFMON enabled:
FBX export prepare: Wrapping Objects... Done (0.000028 sec) FBX export prepare: Wrapping Data (lamps, cameras, empties)... Done (0.000014 sec) FBX export prepare: Wrapping Meshes... Done (0.000022 sec) FBX export prepare: Wrapping ShapeKeys... Done (0.000008 sec) FBX export prepare: Wrapping Armatures... Done (0.000013 sec) FBX export prepare: Wrapping World... Done (0.000011 sec) FBX export prepare: Wrapping Materials... Done (0.000014 sec) FBX export prepare: Wrapping Textures... Done (0.000235 sec) FBX export prepare: Wrapping Animations... Done (0.000011 sec) FBX export prepare: Generating templates... Done (0.000029 sec) FBX export prepare: Generating Connections... Done (0.000040 sec) FBX export fetch empties (0)... Done (0.000007 sec) FBX export fetch lamps (0)... Done (0.000008 sec) FBX export fetch cameras (0)... Done (0.000008 sec) FBX export fetch meshes (1)... Done (1.570453 sec) FBX export fetch objects (1)... Done (0.000220 sec) FBX export fetch remaining... Done (0.001314 sec) FBX export fetch animations... Done (0.000016 sec) export finished in 1.5777 sec.