I'll put this out here just for the sake of example, as I'm pretty sure there are more feats that have this requirement... but I was looking at the guided hand feat.
Prerequisite: Channel energy class feature, Channel Smite, proficiency with your deity’s favored weapon.
Benefit: With your deity’s favored weapon, you can use your Wisdom modifier instead of your Strength or Dexterity modifier on attack rolls.
Obviously, this is nice for clerics. They get all the requirements pretty quick and easily, and they can start wacking their opponents using their wise minds instead of their innate ability to wack things with their strength.
Neat.
But what about non-clerics? There are quite a few classes that get channel energy, but the class ability of proficiency with your diety's favored weapon is a bit more rare.
But is said class ability really the requirement here? Or do you just need to be able to weild the weapon?
For instance, a shaman with the life spirit gets channel energy. They're profficient with daggers... Could Pharasma as diety be an option to get guided hand to work?
On top of that, a FAQ from paizo already claims the class ability can grant unarmed strike. Does anyone who follows Irori and has improved unarmed strike (and the other requirements for this feat) also qualify for guided hand?
The prereqs just say 'proficiency with your deity’s favored weapon', not any particular means of gaining that. A shaman with the life spirit doesn't sound much like a worshiper of Pharasma, but if they are and they have channel smite they seem to be OK for this feat.
With Irori you don't even need the IUS feat (though I'd recommend it), you just need to be proficient with unarmed strikes. Which are a simple weapon at most.
The feat doesn't ask for "proficiency with your deity's favored weapon beign granted by a class", but only that the character has that proficiency. Basically, "deity’s favored weapon" is a variable. For a follower of Pharasma, the prereq line basically says "proficient with daggers".
It doesn't matter how the character is proficient with the weapon, just that they are. A Life Shaman of Pharasma (which is weird flavor wise!) is proficient with their deity's favored weapon, and (unless your GM is a jerk), if they have Channel Smite, qualifies for Guided Hand.
With Irori you don't even need the IUS feat (though I'd recommend it), you just need to be proficient with unarmed strikes. Which are a simple weapon at most.
"All characters are proficient with unarmed strikes" CRB pg. 141
Thanks for the clarification, I wasn't sure.