Starting a list here for deprecated and/or unsupported ways for inhibiting screensaver or suspend. Could move to part of docs some day.

Gnome: gnome-screensaver-command --poke

• Deprecated since Ubuntu 9.10 (Karmic Koala, released 2009)
• The "--poke" argument has been removed from gnome-screensaver 3

Quote from https://wiki.ubuntu.com/DebuggingScreenLocking/HowScreenLockingWorks:

Screensaver Inhibiting
Prior to Karmic, applications that wished to temporarily suspend the screensaver from coming up could periodically send the "poke" command to gnome-screensaver, either using the DBus API, or with the gnome-screensaver-command tool. This would cause gnome-screensaver to reset the idle counter, preventing it from reaching the preset value.

Beginning with Karmic, the proper way to suspend the screensaver is to use the gnome-screensaver DBus API "Inhibit" method. (Ref.: gnome-screensaver FAQ)

Unfortunately, many applications such as VLC, Mplayer and xdg-screensaver still use the "poke" command, which was deprecated and disabled in the current gnome-screensaver codebase. See the following bugs for more information:

https://bugzilla.gnome.org/show_bug.cgi?id=579430

https://bugs.edge.launchpad.net/gnome-screensaver/+bug/428884

systemd-inhibit

Using systemd-inhibit as a heartbeat is not supported: System will start sleep even with:

In [11]: for i in range(10_000):
    ...:     print(i)
    ...:     subprocess.run(
    ...:         ["systemd-inhibit", "--what=idle:sleep", "sleep", "1"],
    ...:         stdout=sys.stdout,
    ...:         stderr=subprocess.PIPE,
    ...:     )

Running systemd-inhibit as long running process is potentially risky (what happens if the python process dies abruptly?). Probably should not be a supported method.