Revit Family Editor - Lock Column

While working in the Family Editor, have you wondered what was the purpose of the Lock column in the Family Types dialog? I have often wondered what this column, first introduced in the 2011 release, does, and was never able to find anything about it in the Help. Today, thanks to a link posted by Richard Black in this thread in the AUGI Revit Architecture - Families Forum, I was able to watch this video, which does a good job of explaining what effect locking a dimension parameter has.