Dynamic memory allocation X vector

I was studying this subject in C, and in most places I'm looking for, one of the examples of using this feature is when you're going to create a vector whose size you do not know. Example:

int main() {

    int num = 0, i = 0, *vetor;

    printf("Digite a quantidade de números que deseja armazenar: \n");
    scanf("%d", &num);

    vetor = (int *) malloc(sizeof(int) * num);

    for(; i < num; i++) {
        printf("Digite um valor inteiro para o %dº elemento do vetor: \n", i);
        scanf("%d", &vetor[i]);
    }

    for (i = 0; i < num; i++) {
        printf("O %dº elemento do vetor é: %d\n", i, vetor[i]);
    }

    free(vetor);

    return 0;
}

But, I can rewrite the program as follows, without using dynamic allocation, and it will continue to work:

int main() {

    int num, i = 0;

    printf("Digite a quantidade de números que deseja armazenar:\n");
    scanf("%d", &num);

    int vetor[num];

    for (; i < num; i++) {
        printf("Digite um valor inteiro para o %dº elemento do vetor: \n", i);
        scanf("%d", &vetor[i]);
    }

    for (i = 0; i < num; i++) {
        printf("O %dº elemento do vetor é: %d\n", i, vetor[i]);
    }

    return 0;
}

What is the difference that dynamic allocation makes in this case? Is there a situation where you have no alternative but to allocate dynamically? And what would be the difference between these two?

vetor = (int *) malloc(sizeof(int) * num);


vetor = malloc(sizeof(int) * num);