ios - https 使用自签名证书的问题

对于https 使用自签名证书，我有如下几个疑问：

1.网上看的资料对于自签名证书都需要在客户端倒入证书，然后验证证书的，如果不验证证书，直接使用发过来的发过来的凭证进行通信有什么风险和问题？

- (void)connection:(NSURLConnection *)connection willSendRequestForAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge {
    //1)获取trust object
    SecTrustRef trust = challenge.protectionSpace.serverTrust;
    NSURLCredential *cred = [NSURLCredential credentialForTrust:trust];
        [challenge.sender useCredential:cred forAuthenticationChallenge:challenge];
  }

1. 我经常在网上看到这样一段代码，你觉得这段代码是怎样验证的？

 NSURLSessionAuthChallengeDisposition disposition = NSURLSessionAuthChallengePerformDefaultHandling;
    __block NSURLCredential *credential = nil;
    if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {
        disposition = NSURLSessionAuthChallengeUseCredential;
        credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];
    } else {
        disposition = NSURLSessionAuthChallengePerformDefaultHandling;
    }
    
    if (completionHandler) {
        completionHandler(disposition, credential);
    }