why is there a buffer for StreamReader Object at all?

new StreamReader(new FileStream("C:/Users/User/Desktop/Testing/RedirectIn.txt", FileMode.OpenOrCreate,
                           FileAccess.ReadWrite, FileShare.None, 128, FileOptions.None), Encoding.UTF8, true, 5, false)

In the snippet above I specify the buffer size as 5.
I mean I underastand why you need to specify buffer size when creating a StreamWriter, but I can not Understand why do I have to specify it when creating a StreamReader.
I can only imagine that since I set it to 5 and I call this 5 times, the buffer gets cleaned up

        Console.In.Read();
        Console.In.Read();
        Console.In.Read();
        Console.In.Read();
        Console.In.Read();
    

Am I correct?