The following paragraph from sndio(7)
probably no longer applies as is:
DEFAULTS
If default is used as the audio device, the program will use
the one specified in the AUDIODEVICE environment variable. If
it is not set, the program first tries to connect to snd/0.
If that fails, it then tries to use rsnd/0. This allows the
sndiod(8) audio server to be used by default and the raw
hardware as fallback; programs don't have to be reconfigured
when sndiod(8) is started or stopped.
With the recent audio(4)/midi(4) change
(as described at http://www.openbsd.org/faq/upgrade67.html)
users cannot access the raw devices any more, so e.g.
$ aucat -o /tmp/file.wav
^C
$ doas rcctl stop sndiod
sndiod(ok)
$ aucat -o /tmp/file.wav
default: couldn't open audio device
instead of falling back to rsnd/0.
(I'll leave the rewording to Alexandre.)
Jan