The purpose of providing the target schema in `S.transform`

pipe(
   S.string,
   S.transform(
      // Why do I need this? Is it just so that S.To<> and S.From<> can calculate the type correctly?
      S.array(S.string),

     // I understand why I need to provide these, of course
      str => str.split(":"),
      arr => arr.join(":"),
   ),
)