I don't think it does unless you reach some odd answers. The answer could be "to create a world that feels real and inclusive." A big part of world building is describing places and characters so those descriptions do matter and are not just made for no reason. I don't need to justify some convoluted way that a healing spell doesn't work.
I think we agree though (?), because if a player asked me so bluntly it would probably require a pause to talk it out at the least, and tbh that's on me for trying to be pithy rather than adding a sentence to clarify.
Yeah, sorry, I should have linked diegetic essentialism.
The easy example I've seen used is Vampires and Werewolves.
How do you kill a vampire?
Vampires are not real.Within the fantasy world vampires can be understood in their relation to their 'in universe' opposite: werewolves. They are essentially the same creature: 'monster that bites you and you turn into one'. Vampires tend to be rich or aristocrats with massive amounts of control over other creatures, environment, etc. Werewolves are poor, often homeless, and lose control over themselves in a bestial form.
How do you kill a vampire, a monster representing wealth, greed, etc.
A simple wooden stake, the tool of peasant farmers.How do you kill a werewolf, a monster representing poverty, desperation, etc
A silver bullet, a weapon literally made of money.