Related Tossup-Bonus is a feature that is common
in a lot of high school formats and is a component
in one of the sections of PACE NSC play. What I have
liked about related tossup-bonus is that the bonus is
truly a gauge of depth of knowledge for the particular
item asked (usually).
Of course, we also don't
necessarily have to link the subject directly. We have plenty
of examples where the bonus was very tenuously
related to the tossup. But to avoid having your bonus go
for nothing, writers are forced to write their
tossups "easier" and that makes the game more fun. Or it
should.