InstrumentationTestRunner: What does android:functionalTest achieve?

I am wondering what InstrumentationInfo#functionalTes开发者_开发知识库t is supposed to achieve. Does it have any impact on how the application environment is started?

I asked this question on the Android issue tracker (unfortunately I can't find the ticket anymore), and a Google rep answered and said: this attribute is not implemented, reserved for future use, and hence, does nothing at the moment.