The one feature LESS has that overpowers SASS

As CSS becomes stronger, and adopts more features, preprocessors diminish, like jQuery helped redefine JavaScript DOM before it went to its death bed.

The way LESS and CSS differ in defining mixins, is probably the one that will take SASS to its bed, earlier! In addition to the unusual choice to complicate syntax, and documentation.

@mixin boldtext {
  font-wieght: bold;
}

// the style
.boldtext {
  @include boldtext;
}

// reusuing it
.myclass {
   @include boldtext;
}

In less:

// the style
.boldtext {
  font-weight: bold;
}

// reusing it, this simple
.myclass {
  .boldtext();
}

Thus, using SASS or LESS by any smart developer, should be limited to the features that CSS does not yet provide, but it might one day.

SASS looks like it has more features, and a lot of new comers are jumping into it, Bootstrap, the bloated CSS framework recently adopted it, making it look like a Lamborghini, except that under the hood, it's just a Prius.

SASS overcomplexity is going to kill it

The one feature LESS has that overpowers SASS