Understanding the use of `unsafe-` and `safe-` functions in Effect TypeScript library internals

/** @internal */
export const renderStream = <A>(self: DocStream.DocStream<A>): string => Effect.runSync(renderSafe(self))

const renderSafe = <A>(self: DocStream.DocStream<A>): Effect.Effect<string> => {
// ... can throw or Effect.succeed
}

// Or

/** @internal */
export const foldMap = dual<
  <A, M>(M: monoid.Monoid<M>, f: (a: A) => M) => (self: DocTree.DocTree<A>) => M,
  <A, M>(self: DocTree.DocTree<A>, M: monoid.Monoid<M>, f: (a: A) => M) => M
>(3, (self, M, f) => Effect.runSync(foldMapSafe(self, M, f)))

const foldMapSafe = <A, M>(
  self: DocTree.DocTree<A>,
  M: monoid.Monoid<M>,
  f: (a: A) => M
): Effect.Effect<M> => {
// ... can only Effect.succeed
}