So I just realized that you can take Harmonic Spell at first level and then use your swift action every round to cast Vacuous Vessel every round to keep you bard/skald song up for free. You would not be able to changed performances because you already used your swift action but a level 10 Skald with Skald's Vigor, Greater would be able to heal the party to full health after every combat.
Technically Vacuous Vessel is a cantrip not a spell. They are listed as a separate class feature and do not show up on the spells per day table for the bard. As a GM I would say that harmonic spell only works with an actual spell.
Most GMs are not going to allow this anyways. The above reason gives an excuse of why it is not allowed. It is a little bit shady but so it trying to use an obviously unintended exploit.
If you do some searching on this topic there is a rare post from James Jacobs wherein he states something as official errata, he says it must be a 1st level spell or higher. For whatever that is worth to you/ your GM.
Defiantly a shady excuse to not allow it. As the description of Cantrip considering how many times Cantrips are described as spells in the Class Feature.
Thanks for the clarity on why I have not seen people using this before.
just like to point out that even if this is allowed by your gm it would still need 1 round of bardic performance to start it (the feat let you maintain a performance that is already going not start one).
and then you have to keep talking (V spell comp) and touching your pocket every 6 seconds without stopping the performance to keep it up. some1 might call in the guards if you do that...
Technically Vacuous Vessel is a cantrip not a spell.
This is completely false. Cantrips are spells, and count as such for everything.
"Cantrips: Bards learn a number of cantrips, or 0-level spells, as noted on Table 3–4 under “Spells Known.” These spells are cast like any other spell, but they do not consume any slots and may be used again." CRB pg. 38, emphasis mine.
You would not be able to changed performances because you already used your swift action but a level 10 Skald with Skald's Vigor, Greater would be able to heal the party to full health after every combat.
Boots of the Earth can provide infinite healing for 5k. Glorious Heat is another feat that can be (ab)used with 0th level spells to provide infinite healing. Both Harmonic Spell and Glorious Heat recieved PFS campaign clarifications changing them, but neither recieved an FAQ.
Ultimately, at 11th level, healing isn't that hard to come by. Low level level spell slots are cheap, and performance rounds are plenty, and thus it takes quite a lot of damage taken in a day before Harmonic Spell saves you recources that are actually valuable. And don't forget, a feat is a notable investment, especially when it only does something in combination with two other feats, on a class with no bonus feats. That means half the Skald's feats at 11th level spend just on the healing.
The Skald is also not that popular a class, and this combination does only work with the normal Inspire Rage (and not one of the archetypes that replace it, like Wyrm Singer), which does nothing (in combat) for dex-based builds, cha-based builds, Barbarians, Bloodragers, Kineticists, and casters. That makes the Skald hard to fit in many parties.