Understanding of "WhoAmIRequest"

Hello

I am working with WhoAmIRequest class of CRM SDK.

When I use following snippet:

 WhoAmIRequest who = new WhoAmIRequest();
 WhoAmIResponse whoResp = (WhoAmIResponse)crmService.Execute(who);

I get the reference to theonly systemuser I have defined for my test crm organization.

Now this is a test environment, but in production we have multiple users of CRM.

What I am trying to understand is that in production environment how WhoAmIRequest  will work, as well as which user will be returned in the WhoAmIResponse ?

Regards