The model 33 had a very fast and powerful carriage return mechanism,
good for cracking walnuts, but it took up to two character times to
complete a CR. If you didn't send two non-printing characters (such
as NUL), you risked having your character struck somewhere in the
middle of the line.
That was not my experience. I cut my teeth on a PDP-8/M running OS/8 with an ASR-33 attached and directly programming the KE8E controller without any additional time-delay loops. Outputting additional NULs would have screwed up binary paper tape output, so that can't have been how it was done.