Is that what OP is talking about?

It is a *A wide benefit that *S has priority on waiting lists. That and the 'priority stand-by' are basically the only 'benefits' of *S making it by far the worst alliance-wide elite tier.
I mean, as someone who has been *G for more than a decade, I have never really understood this benefit. If you want to make a reservation, but your preferred class of service is unavailable, you have priority apparently, not including award tickets. But I don't really know how I would ask to get on this waiting list or if all airlines even offer such a thing. At least the standby one, I presume means if your flight is cancelled and you have to standby for later flights, you have priority. This could certainly be beneficial when it comes up. But the priority waitlist one is one I have never really understood.