Why warn unhandled exception

main.dart

void main() async {
  final a = Future.delayed(const Duration(seconds: 1));
  final b = Future.error(2);
  try {
    await Future.wait([a, b]); // Warn uncatched error if remove this line.
    await a;
    await b;
  } catch (e) {
    print(e);
  }
}