At my school the 150 would also be flown overweight. Two adults and full fuel. Rationale when I mentioned this after learning about M&B: a few kg overweight doesn't bring the plane down, running out of fuel on cross country does. Center of gravity was within limits. The runway was very long, so we would already be at a few hundred feet before the end of the runway. Of course on paper everything was within legal limits and if we would get an inspection they would never check the remaining fuel... As a fresh student I believed their story, and without proper leaning it used much more fuel than the book said. A dubious safety measure.