3.A scratch pad can be very useful not just for temporary elisp code
but for any scratch notes or programing in other languages. (For
example, well known programer Stevey Yegg in his popular blog article
Effective Emacs↗, considers creating new temp buffer as a top 10 tip
in emacs productivity.)
I agree. The scratch buffer seems to be made so you could easily type
and execute lisp code interactively. But even if you just want to run
one lisp command, you can type it literally anywhere and type C-x C-e
(the disadvantage is you won't get syntax highlighting or completion
if you are not in lisp-mode). IMHO, *scratch* should default to
text-mode.