MPlane command is useless because Rhino cannot use the construction planes made by the MPlane command.
I don’t understand your comment. Can you provide any more details?
Here is help for MPlane if you need:
@dale You are right. The MPlane command does work - it does change “active” construction plane. I was confused because I use NamedView command a lot. I did not know that NamedView command restores old construction plane. (Rhino help file does not explain the fact that the NamedView command saves and restores “active” construction plane.)
The best way to prevent this confusion is combining NamedView and NamedCPlane into single command.
Every time you move, rotate, or scale object connected to the mobile construction plane (or type MPlane Refresh), the mobile construction plane becomes “active” construction plane.
This is an option (which you can turn off):
Given the above I don’t think this is necessary.