为啥要收到才能走？

6月5日485 filed..打算回国签H4，律师建议收到receipt of notice再走，不懂为啥，原文如下：

"We will be in contact with you when the receipt notices are received
(2-3 weeks). As a reminder, we recommend that you do not travel outside of
the U.S. until after the receipt notices have arrived."

2-3 weeks可以等的，但就怕过了3个星期这receipt of notice也未必收到，而且律师说打手印会在1个半月到两个月间，有这么快吗？看坛子里的人好像比这个时间要晚阿。实在是不好决定时间回去，可这日益严重的颈椎病又不等人。

查了旧贴，看到xiaobaitu说只要移民局收到485的申请即可以离境。

谢谢大家！