Yes. For example, in a race your fastest lap might be with a heavy draft effect, so the delta time is pretty much useless then.
But if i could manually choose a lap which would work as a reference lap showing the delta, it would be very useful. Say, give a 10-20 second delay after the lap, and if i press the "reference" button then, the delta time will compare to the lap i just completed.
Am i making any sense?