What's the point of using composition when the composed class is only used at a single place?

I see some code design like this

class my_class:
  def __init__(self, arg1, arg2, arg3)
    self.data = data(arg1, arg2, arg2)
    # initialize some other attributes

# the only place data class is used is in my_class
class data:
  def __init__(self, arg1, arg2, arg3)
    self.arg1 = arg1
    self.arg2 = arg2
    self.arg3 = arg3

I don't see the point of doing that, when you can just do

class my_class:
  def __init__(self, arg1, arg2, arg3)
    self.arg1 = arg1
    self.arg2 = arg2
    self.arg3 = arg3
    # initialize some other attributes

which gets rid of the seemingly unnecessary layer.

Is there some advantage of design standard that motivates the former design?