SASS, imo, is a much more mature and interoperable language.

Compare

.mixin (@a) when (lightness(@a) >= 50%) {

   display: none;

}

to

@if $boolean

    @debug "$boolean is #{$boolean}"

    display: block

  @else

    @debug "$boolean is #{$boolean}"

    display: none

Note, also, that there's a logger.