Return using this pointer vs return by value

What is the difference between returning a this pointer and return by value.

I will try to explain my case with a example..

I have the following code

#include <iostream>
using namespace std;

class Count
{
    private:

        int count;      

    public:

        //Constructor
        Count():count(0) { cout << "Constructor called" << endl; }

        Count(Count& C):count(C.count)
        {  
            cout << "Copy constructor called" << endl; 
        }

        //Destructor
        ~Count() { cout << "Destructor called" << endl; }

        Count  operator ++ () {
            count++;
            Count temp;
            temp.count = count;
            return temp;
            //return *this;

        }

        //Display the value.
         void display() { 
            cout << "The value of count is " << count << endl; 
        }

};

int main()
{
Count C;
Count D;
C.display();
D.display();
D=++C;
C.display();
D.display();
return 0;
}

I have the following function in a class

Count  operator ++ () {
        count++;
        Count temp;
        temp.count = count;
        return temp;
}

when I use the above function, I see that the normal constructor is called when returning the value.

But I change the function as below

Count  operator ++ () {
        count++;
        return *this;
}

The above function calls the copy constructor when returning this pointer.

Can someone help me understand the difference.