When should sizing grip (windows Forms) be used?

Should it be used for all sizable forms, or only when it is not easy to guess that a form is sizable? Is there a GUI convention to use it?

Any link to a documentation would be appreciated.

From stackoverflow

• According to the Vista User Experience Guidelines:

  Resizable windows no longer must show the resize glyph in the lower-right corner, because:

  • All sides and edges of a window are resizable, not just the lower-right corner.
  • The glyph requires a status bar to display, yet many resizable windows don't provide status bars.
  • The resizable window borders and resize pointers are more effective at communicating that a window is resizable than the resize glyph.

  http://msdn.microsoft.com/en-us/library/aa511262.aspx