I’ve seen the advantages firsthand. The test guys would drive across town and pick up some chips hot off the fab, put them on the scope under various conditions, and then be pushing updates in a day or two. The designer could actually sit with the test guy and fiddle with the tests to understand the problem better, and then walk upstairs and mess with the simulator. None of this can happen at nearly the fluidity or speed when you’re designing, producing, dicing, packaging, and testing the chips all in different time zones.