Is it necessary/recommend/best practice/any other positive to use only one server environment to perform all development, unit testing and QA?

If so, is it then wise/part of Agile to then have only one staging environment before Live?

Considering that this could mean internationally distributed teams of developers and testers in different time zones is this wise?

_{This is something being implemented by our QA manager. The opinion put forward is that doing all the dev and testing on a single server is "Agile." The staging environment would be a second environment, and then live.}