AccessController.doPrivileged到底什么时候才能用到？

Question

我看到代码里面大量出现AccessController.doPrivileged 相关的代码

public static InetAddress addressByName(final String hostname) throws UnknownHostException {
    try {
        return AccessController.doPrivileged(new PrivilegedExceptionAction<InetAddress>() {
            @Override
            public InetAddress run() throws UnknownHostException {
                return InetAddress.getByName(hostname);
            }
        });
    } catch (PrivilegedActionException e) {
        throw (UnknownHostException) e.getCause();
    }
}

我目前不清楚的是：什么时候才能用到，我不写这个AccessController.doPrivileged会有什么问题？有大佬可以举个例子吗？