bug#16630: desktop-auto-save seems confusing

[Glenn Morris]

Package: emacs
Version: 24.3.50

desktop-auto-save has what seems to me to be confusing, limited functionality.

emacs -Q   ; no existing desktop
M-x desktop-save-mode
C-h v desktop-auto-save-timer
   -> nil

M-x customize-variable RET desktop-auto-save-timeout RET
  Set to 20, set for current session

C-h v desktop-auto-save-timer
  -> no longer nil, but still does not auto-save anything,
     because desktop-owner returns nil


Basically, it seems that the only way this feature does anything is if
you enable (desktop-save-mode) in .emacs AND have a pre-existing desktop
file when you start Emacs.

Why doesn't enabling desktop-save-mode at any time just turn it on?
Why does it require the desktop file to exist beforehand?