When to use pointer as parameter in function c++?

Question

I'm a beginner in C++. I think I understand pointers and references, and started using them as parameters to functions.

Is there ever a time for a function parameter to be a pointer, when a reference is less work and is easier to understand?

For example, using a pointer as parameter:

#include <iostream>

using namespace std;

void add_one(int *x);

int main() {
    int a = 0;
    add_one(&a);
    cout << a << "\n";
    add_one(&a);
    cout << a << "\n";
    add_one(&a);
    cout << a << "\n";
}

void add_one(int *x) {
    *x += 1;
}

versus a reference as parameter:

#include <iostream>

using namespace std;

void add_one(int &x);

int main() {
    int a = 0;
    add_one(a);
    cout << a << "\n";
    add_one(a);
    cout << a << "\n";
    add_one(a);
    cout << a << "\n";
}

void add_one(int &x) {
    x += 1;
}