What does morale really do?

[No, I'm not, You are!]

Am I just bad at googling? The only thing I can find about the effects of morale is that negative morale has no effects and positive morale gives XP increase bonus.

Is that it? Cause I honestly find that completely neglectable. Even on Lethal. Xp boost seems like a luxery to me, not a must have.

[Tax evasion]

Low morale will lead to the following consequences:
1. Conflict between 2 survivors in your community (one instigator and one victim). The instigator will have their morale temporarily reduced by 7, while the victim's morale will be temporarily reduced by 15.
2. Survivors in your community will sometimes waste food/meds/ammo/materials/fuel rucksacks, this will temporarily improve their morale. This applies even to survivors who don't have "sometimes wastes resources" as their traits.
3. If a survivor's morale becomes low enough, they will become frustrated and threaten to leave your community. If they stay frustrated for too long they will leave your community and they will leave for good.

You can read further in https://state-of-decay-2.fandom.com/wiki/Community_Morale

[Protectron]

Low morale also severely slows down building time and facility action times, as well as lowering XP rates.

Good and in particular enthusiastic morale greatly speeds up building and facility action times, increases XP rates and as a random event you may get rare and high-quality items.

None of this matters in Green, normal and Dread difficulty levels, as the penalties are largely irrelevant there. In Nightmare and particularly Lethal, the penalties are severe enough that it affects gameplay.