I was wondering what was the difference between : 

```
@mixin transition($args...) {
  -webkit-transition: $args;
  -moz-transition: $args;
  -ms-transition: $args;
  -o-transition: $args;
  transition: $args;
}

```

and 

```
@mixin transition($args...) {
  -webkit-transition: #{$args};
  -moz-transition: #{$args};
  -ms-transition: #{$args};
  -o-transition: #{$args};
  transition: #{$args};
}

```

what is the purpose of having an # in front of the argument ?