In a language with significant newlines you need both comment-with-splice and comment-without-splice - the latter so that you can add a comment without affecting the meaning of the layout. For example, I might have a makefile containing

OUTPS=${SRC:.tex=.ps}
OUTPDF=${SRC:.tex=.pdf}
OUTDVI=${SRC:.tex=.dvi}

And I should be able to comment out any of those lines without inadvertently concatenating them.