I'm actually a bit of a fan of whitespace in code. I know a lot of people who…are of a different opinion, to say the least. Perhaps it's because I don't have some of the more sophisticated code-motion keys down in Emacs, but I like to have the whitespace to break up semantic units and help me understand how lines of code are interrelated.
So it's surprising that I haven't ever really cottoned to
C-o (open-line).
Actually, that's not 100% true—in the readline library that
underlies the history system in the bash shell, I use C-o a lot; it
is useful for when you have a repeated series of commands you want to
cycle through again, you can find the first command in the series and
then step through with it.
But in Emacs, I've never used it much.
However, what I do find myself doing a lot is
C-q (quoted-insert) C-j (newline-and-indent) in the mini-buffer,
during search-and-replace sessions. And for that, C-o may be, at
times, an easier option. So I'll try and adopt it, and see how it goes.