在API调用中使用系统时间戳

Question

我想知道添加系统时间戳在验证API调用时有什么用处。例如，来自亚马逊的一项服务：

https://mechanicalturk.amazonaws.com/
?Service=AWSMechanicalTurkRequester
&AWSAccessKeyId=[the Requester's Access Key ID]
&Version=2013-11-15
&Operation=ApproveAssignment
&Signature=[signature for this request]
&Timestamp=[your system's local time]
&AssignmentId=123RVWYBAZW00EXAMPLE456RVWYBAZW00EXAMPLE

添加系统的本地时间有什么好处？这会比以下更好：

https://mechanicalturk.amazonaws.com/
&AWSAccessKeyId=[the Requester's Access Key ID]
&Signature=[signature for this request]
&OTHER_PARAMS...