we do roads that have sometime 3 controlled layers all with survey verification and compaction and depth tests, if the plan says 130mm thicks layer and it gets tested and its 110 we gota rip it up and go again...so having machine control from subgrade, then sub base, then 2 layer base, makes it easy to control. not so much for quality of work as many grader drivers know you dont rely on the machine guidance to do that, but just making sure of the corect layers and lines it is a handy piece of gear we have Trimble GCS900 on a 140m