Full description
Emacs is more of an "environment" than just an editor, since it has the
strong configuration language, emacs-lisp. There are a lot of applications
written in emacs-lisp, and you may run many applications on your Emacs at
the same time, i.e. e-mail reader, news reader, IRC client, a kind of IDE,
etc. These applications likely consist of two or more windows, so when you
switch among applications, you may want to save or restore how windows are
located (this is called as "window-configuration"). For this purpose, Emacs
has two functions, window-configuration-to-register and jump-to-register,
but these are too primitive to use on a daily basis.
ElScreen provides the ease-to-use environment to save or restore several
window-configurations.