0_namespacing.scss

mymodule {
  @at-root {
    .#{&}-header { ... }
    .#{&}-footer { ... }
    .#{&}-body   {
      a          { ... } 
      span       { ... } 
      p          { ... } 
    }
  }
}

1_namespacing_output.css

.mymodule-header { ... }
.mymodule-footer { ... }
.mymodule-body a { ... }
.mymodule-body span { ... }
.mymodule-body p { ... }

Can someone please give another example of how namespacing might be used--thanks @aceofspades, I just would like to see it in another context.