You're right, an LLM doesn't have preferences. As shorthand, I thought it a useful concept though, as they do have particular ways of writing that can be tuned for.

The effect system here is part of a type system (technically a type-and-effect system). Where a value type typically describes what value a computation returns, an effect describes which operations it can perform during evaluation.

The difference is that effects propagate through the call graph, so lower-level code cannot access disallowed resources without that authority appearing higher up. At runtime, world effects also require an explicit grant. In a typical value type system, lower-level code can introduce side effects without them appearing in the caller’s type.