There are rare instances where a the intermediate circuit can be useful, but most will never need it. The intermediate circuit was designed specifically for an IR manifold, and can be useful on a 4 or 6 cylinder comp engine where plenum pulsing is high enough to disrupt low RPM and part throttle booster signal. On an occasion it can be helpful on an under carb stop, if the engine is large enough to force the stop blades to close too far, but it takes less fuel than most 3 circuit carbs come with to do the trick in those few cases. As far as using it to come up on the converter, if you use a decent booster it's never an issue.