Option.apply の使いどころ

REPL.scala

scala> val f: (Option[Int], Int) => Option[Int] = _ orElse Some(_)
f: (Option[Int], Int) => Option[Int] = <function2>

scala> val seq: Seq[Int] = Seq(1,2,3)
seq: Seq[Int] = List(1, 2, 3)

scala> seq.foldLeft(Some(0))(f)
<console>:10: error: type mismatch;
 found   : (Option[Int], Int) => Option[Int]
 required: (Some[Int], Int) => Some[Int]
              seq.foldLeft(Some(0))(f)
                                    ^

scala> seq.foldLeft(Option(0))(f)
res1: Option[Int] = Some(0)