tp6中自动时间戳怎么使用呢？为什么要使用它呢

<?php
namespace app\index\controller;

use app\BaseController;
use think\facade\Db;
use app\model\Aaa;
use think\facade\Cache;
class Index extends BaseController
{
    public function hello()
    {
    	$user=new Aaa();
    	$user->name="cyg";
    	$user->save();
    }
}

 protected $autoWriteTimestamp = false;