Hmmm, I was reading a discussion on diff settings between 2 drivers in the Porsche GT3 Cup.
The guy towards the very top of the Championship said he prefered a higher decel as it made the car more stable off the throttle on turn in. IIRC correctly, he said it did cause a bit more understeer, but the payoff was being able to brake harder and deeper in to the apex with confidence... which to me would equate to a car that would harder to initiate a drift in?
Hmm that's interesting. However, I think it's important to note that the conditions we are talking about are very different (Porsche GT Cup vs Drifting).
The guy from the Porshe Cup is more than likely right, and you are probably right that a car that is more stable under braking would be harder to initiate a drift in, under braking.
The thing is though (and maybe this is totally just my style, not sure if others would agree), I very rarely initiate under braking. Off the top of my head, I can't think of one corner that I would initiate under braking. Like I said, maybe it's just my drift style, but I always prefer to initiate farther away from entry, under power, and transition through the entry if necessary. Even if there is one specific corner that would require me to initiate under braking, I would more than likely blip the throttle or pull the e-brake to help break traction at the rear. So I guess I'm saying that a high Decel value, which makes initiating under braking difficult, does not affect my drift style.
Transitioning while braking, or off throttle, is another story. Almost every tight corner after a high speed section requires some sort of transition under braking - either left to right (or right left), or high to slow speed multi-apex. But you must keep in mind that traction has already been broken, the car is already drifting, so concerns about initiation are not necessary. Just as a high Decel diff setting stabilizes the car under braking while the rear has traction, it stabilizes the rear while when traction is broken. The actual effect it has is this - a higher Decel value causes the outside rear wheel to gain traction slower, which makes the car change direction slower while drifting (ie, it is more stable). The lower the setting, the faster that outside tire will gain traction, which makes the car change direction quicker. If the setting is too low, and that wheel gains traction too fast, it can cause the car to snap back the other way at a rate that is too quick to "catch".
Most of my drift cars (1100-1300kg) have a Decel value from 45-55. Some of the lighter cars, like my PS13s, I run a setting closer to 60. On the heavier cars, a Decel setting of 60 makes them feel very boat-like during braking transitions. I've also found that most braking transitions are performed in tighter areas, so I prefer the car to be a bit snappy, so I can make the transition quick.
The other thing a lower Decel value does is cause the car to slow down more when you lift off the throttle mid drift, or during transitions. This can be either good or bad, depending on the car. For a high powered, heavy car that picks up a lot of speed while drifting, I would run a lower Decel value to aid in slowing the car down as you approach a slow speed corner. Too low a setting on a lightweight car can cause it to lose too much momentum, thus killing the drift.
Anyways, that's just what I've found through my testing.