Huh? You can't be in Supercruise with FA-off. I'm confused by your post.
As
Ddtdmbow outlined. I only tend to jump FA-on if I'm ignoring scans, even the parent star, which for months has been exceptionally rare given I'm exploring.
I'm not sure it's a 100% sure way of safe jumping (though it's precisely that so far), because you might be jumping into some kind of anomalously tortuous, unholy close-binary or worse combo. However, drops can go bad very quickly with a fraction of a second's loss in concentration, and so when you drop at 30k/ms you have - as Louis Armstrong might put it - all the time in the world [to pick the optimum egress vector].
It's useful for climbing from a planet's surface and entering SC if you're looking to go suborbital and find a different/better landing spot, too, as normally you'd lurch forward, but toggle FA-off before engaging the FSD and you'll enter SC at 30k/ms.
/edit
White dwarfs aren't worth it. The boost is tiny. Neutrons are much better and, in my experience, a lot easier to boost. I think the drop off point on white dwarfs is too close to the edge of the cone. On neutrons it seems like you have more room to maneuver.
I'd rather take the hit of the few hundred jumps and arrive at my destination in one piece than save time - I had a lot of scan data on board, and I've crashed once near the core already... ;-)
I am finding a lot of neutron's on my way to Colonia, though, and barely any seemed to have been claimed.