The Bealach na Ba has a fairly relentless gradient that you need to be in your lowest gear to climb up almost all the way, but as you climb you realise that you might be able to make it all the way without getting off as long as you don't have to stop. If you do have to stop, the gradient will make it pretty difficult to get going again. If you have heavy luggage it will be almost impossible. So there is a great incentive for any cyclist climbing up it, at 3mph or so, not to stop, although it is fairly easy for a single cyclist to allow for one or two cars to pass in the passing places.
If you are in a large group, any passing car is bound to have to stay behind some of the cyclists past several passing bays, even assuming some of the cyclists stop in them each time. If you are cycling in a group, it is not pleasant to have a car stuck in it between you and the rest of the group.
When I cycled up Bealach na Ba, in 2005, I did it on my own and was probably fortunate
that there was thick fog for much of the way. This meant that very few cars were attempting to drive it, and that those that did were not able to drive any faster than I was cycling anyway. It was pretty hair-raising though, as some sharp bends with long drops beside them did seem to rear up out of nowhere.
When I reached Applecross I chatted to a man who had driven over at about the same time, and he did use the term 'most nightmarish drive' to describe it, although he wasn't talking about cyclists. In the fog I imagine that it would have been utterly terrifying to drive, as your all round visibility as a driver is far poorer than as a cyclist, and he would have had no warning whatsoever of the sheer drops that kept appearing. He looked like he was still shaking when I saw him, and that was a few hours after he had come over it.
Cycling single track roads deserves a thread of its own (not hidden on this thread), so I will start one.