Why use self.width in the area method instead of @width?

InheritanceExample.rb

class Shape
  attr_accessor :color
  
  def initialize(color = nil)
    @color = color || 'Red'
  end
  
  def larger_than?(other)
    self.area >= other.area
  end
end

class Rectangle < Shape
  attr_accessor :width, :height
  
  def initialize(width, height, color = nil)
    @width, @height = width, height
    super(color)
  end
  
  def area
    self.width * self.height
  end
end

class Square < Rectangle
  def initialize(side, color = nil)
    super(side, side, color)
  end
end

class Circle < Shape
  attr_accessor :radius
  
  def initialize(radius, color = nil)
    @radius = radius
    super(color)
  end
  
  def area
    Math::PI * self.radius**2
  end
end

TEST WITH:
a= Rectangle.new(1, 2, "Blue")
b= Square.new(5, "Green")
c = Circle.new(7, "Brown")
p c.area
p b.larger_than?(a)
p a.larger_than?(b)