I've seen a lot of heavy nesting caused by the belief that functions should only have one return statement. Ex:

    // Original
    function render() {
      $return = null;
      if($condition1) {
        if($condition2) {
          $return = 2;
        } else {
          $return = 1;
        }
      } elseif($condition3) {
        $return = 3;
      } else {
        $return = 4;
      }
      return $return;
    }

But I'd rather read:

    // Refactored
    function render() {
      if($condition1 && $condition2) return 2;
      if($condition1) return 1;
      if($condition3) return 3;
      return = 4;
    }