In Pathfinder, devils are related to the hierarchy of the Hells and are all positions in the bureaucracy, as the soul works its way up the ranks. Meanwhile demons are all associated with sins committed by the soul in life. Daemons are all created by people who died in horrible ways.
Which adds another layer of differentiation to the evil outsiders.
(But it only works so-so, given the sheer number of fiends in Pathfinder, and the fact it just slaps these ideas atop existing demons and devils. It's a huge lore retcon.)
As mentioned, Pathfinder daemons are also defined for their nihilism. They don't just want to mindlessly destroy like demons, they specifically want to annihilate living things in particularly violent ways. So it's more their sadistic methods. They're fiends with the intelligence and tendency to scheme of devils with the murderous impulses of demons.
Which is fine and all... but doesn't map nicely to Yugoloths.
Looking through the MM, Yugoloths do nicely fit the tropes of Neutral Evil. They're mercenaries who are entirely self serving and have no loyalties to anyone or any cause. They are the embodiment of selfishness. They're avarice opposed to devil's tyranny and demon's anarchy.
The problem is... they're completely and totally motivated by self interests, but we have no idea what those interests are. The Monster Manual and Tome of Foes both mention they work for hire but neglects to mention what they're paid with. Just gold? Diamonds? Magic?
Is it souls? And if so, why? Because it doesn't sound like Yugoloths are interested in making more of themselves (or are even able to do so).
