Не могу понять, почему нужен виртуальный деструктор

// Matrix.h
#include <random>
class Matrix
{
public:
 
    Matrix(int m, int n);
    Matrix & operator = (Matrix const & );
    virtual ~Matrix(); // Вот здесь!!!
    double **ValueMatrix;
 
private:
    int Columns = 0;
    int Rows = 0;
 
};
// Matrix.cpp
Matrix::Matrix(int n, int m) : Columns(n), Rows(m)
{
    std::random_device rd;
    std::mt19937 e2(rd());
    std::uniform_real_distribution<double>dist(-0.5, 0.5);
    ValueMatrix = new double* [Columns];
    for (int i = 0; i < Columns; ++i) {
        ValueMatrix[i] = new double[Rows];
 
        for (int j = 0; j < Rows; ++j) {
            ValueMatrix[i][j] = dist(e2);
        }
    }
 
}
 
Matrix::~Matrix()
{
    int Col = Columns;
    for (int i = 0; i < Columns; ++i)
        delete [] ValueMatrix[i];
}

#include "Matrix.h"
//Network.h
class Network
{
public:
    Network( const int *size,  const int &len);
    ~Network();
private:
    Matrix **wights; 
    int layersN; 
 
};
//Network.cpp
 
#include "Network.h"
 
Network::Network(const int *sizes, const int &len)
{
    layersN = len;
    wights = new Matrix * [layersN-1];
    for (int k = 1; k < layersN; ++k){
        wights[k - 1] = new Matrix(sizes[k], sizes[k - 1]);
    }
}
 
Network::~Network()
{
    for (int i = 0; i < layersN-1; ++i){
        //wights[i]->~Matrix();
        delete [] wights[i];
    }
 
}
 
//main.cpp
 
#include <iostream>
#include "Network.h"
 
int main()
{
    int buf[5] = { 3,7,4,2,4 };
    Network* network = new Network(buf, 5);
    std::cout << "Hello Work!" << std::endl;
    delete network;
    return 0;
}

delete [] wights[i];