C# Switch statement with/without curly brackets.... what's the difference?

Has C# always permitted you to omit curly brackets inside a switch() statement between the case: statements?

What is the effect of omitting them, as javascript programmers often do?

Example:

switch(x)
{
  case OneWay:
  {                               //  <---- Omit this entire line
    int y = 123;
    FindYou(ref y);
    break;
  }                               //  <---- Omit this entire line
  case TheOther:
  {                               //  <---- Omit this entire line
    double y = 456.7; // legal!
    GetchaGetcha(ref y);
    break;
  }                               //  <---- Omit this entire line
}