From the other side of the debate, what can be frustrating (in particular on a busy day) is the student who insists on conducting a Star Annual as a pre-flight. Once bloggs has put his spanners away its nearly time for the next lesson! A chance to enjoy a 3 course meal perhaps, or even have another cigarette.
In all seriousness though i prefer it that way round than the pre flight consisting of just checking the door opens and the seat supports your weight before we start.
As Duir says, it gradually gives the student more of the aeroplane more of the time.