ido-use-virtual-buffers

ido-use-virtual-buffers is a variable defined in `ido.el'.
Its value is

nil

Documentation:
If non-nil, refer to past ("virtual") buffers as well as existing ones.
The options are:
nil: Do not use virtual buffers.
t: Always use virtual buffers.
auto: Use virtual buffers if the current input matches no existing buffer.

Essentially it works as follows: Say you are visiting a file and
the buffer gets cleaned up by midnight.el. Later, you want to
switch to that buffer, but find it's no longer open. With virtual
buffers enabled, the buffer name stays in the buffer list (using
the `ido-virtual' face, and always at the end), and if you select
it, it opens the file back up again. This allows you to think
less about whether recently opened files are still open or not.
Most of the time you can quit Emacs, restart, and then switch to
a file buffer that was previously open as if it still were.

This feature relies upon the `recentf' package, which will be
enabled if this variable is configured to a non-nil value.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.