https://wiki.debian.org/Festival

The wiki documents it's use for writing a wav file to disk, there are many
potential uses for it that don't involve local sound output such as sending
audio from a web server for example.  I think a recommends is a reasonable
option here.

The default /etc/festival.scm uses "aplay" from alsa-utils to play audio,
that can easily be configured to use "paplay" from pulseaudio-utils or
"pw-play" from pipewire-bin so depending on
alsa-utils | pulseaudio-utils | pipewire-bin would also be a reasonable
option.

The counter argument to this would be "pulseaudio and pipewire both provide
an ALSA interface so an ALSA program can talk to all three".  But I think
that as both KDE and GNOME depend on pipewire-bin the vast majority of
systems will have a more recent sound system installed and not wanting to
have alsa utilities installed is quite reasonable.

Even going a single step up and depending on pulseaudio-utils would be a
step up.

In Testing the only packages that depend on alsa-utils are festival
and reform-desktop.