C++ :: Pointer Usage To Base Class Object In Vector Int Main Function

I know what are pointer's and how to use them but there is one point i am not able to understand. Below is the example code

I understand everything in the below code except 1 thing why i am using pointer to base class object in vector int the main() Function?

Code:
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
// base class

[Code] ...

Here is the lines of code i want to understand.

Code:
vector<Employee*> employees;
employees.push_back(&emp1);
employees.push_back(&mgr1);

I know if i will not use the pointer base class function "virtual double grossPay" will be called for both base class object and derived class object and when i will use pointer with reference to the object because base class function is virtual it will look for same function in derived class and if available it will execute it.