title: Play Framework, Format[A] vs OFormat[A]
body: <p>I can't find an explanation in the Play Framework docs.
  I found this <a href="https://stackoverflow.com/questions/32289702/play-framework-2-4-writes-a-vs-owrites-a-formata-vs-oformata-purpose">question</a> but now I can't see why will I use Format[A] at all.</p>