There seem to be three benefits.
First, that originally pursued by the US Palma Teams - to reduce velocity spreads. So, most top F/TR shooters are now using these cases even with 155s and faster burning powders such as 8208 XBR and H4895. The exhaustive tests those teams carried out suggested a third reduction in ES / SD with the 155gn Palma MK and VarGet, and I'd reckon that's a fair assessment of what happens in this and similar combinations.
Second, the velocity issue. This was most appreciated here in the UK initially by the 210gn enthusiasts in F/TR. No doubt about it, if you want to shoot 200s and heavier with slow-burning powders (by 308 standards), these are the cases to use. 210s, and now for the minority who've adopted them, the 200gn, 215gn and 230gn Berger Hybrids are being driven to very impressive MVs using Viht N550, and less frequently Alliant Re17 without any nasty or unwanted side effects. Early on, the sceptics said that these loads must be running at proof level pressures and that woe would ultimately afflict the sinners, but not at all after two if not three seasons. My personal opinion - no proof - is that the combination, of which the small flash-hole is a key element, changes the charge burn pattern in some way for the better, maybe flattening and extending the pressure curve.
Third the life issue. When I shot 155gn Scenars at ~3,075 fps using N540 and then 185gn Berger BTs at ~2,800 fps over N550 from a 30-inch suitably throated barrel, I'd either junk or relagate to lower pressure short-range loads standard Lapua or Norma brass at five to six firings with primer pockets now on the loose side. Running the 155.5gn Berger BT at 3,050 fps over 8208 XBR in small primer brass, I'm at half a dozen firings with some case lots and pockets are subjectively as tight as when new. Reputedly, some of the early heavy bullet adopters are now well into double figures on loadings and not seeing any problems at all. Lapua Palma brass is the best argument I know for case annealing - the front end will need attention long before the back end wears out.
So far as extraction problems go, I've not had any, and I've not heard of any to date from others. But, I've yet to pass the half dozen firings mark, and my 155.5/3,050 fps load is mild compared to many being currently used.
Temperature wise, I get nervous about Palma brass loads when the thermometer dips to around 5-deg C. However, I suspect this is at least partly affected by powder choice. The US Palma Teams tests included putting (155 / VarGet) ammo in a freezer overnight and still getting good results. With my original Viht tests, N150 was unaffected by ambient temperatures ~2-3-deg C while N140 and N550 were. I suspect that ADI / Hodgdon powders (including IMR-8208 XBR) aren't particularly (cold) temperature affected so this brass will still work fine just above freezing.
Most F/TR shooters here using this brass prime it with the F205M. I've used the CCI-BR4 alone. I have a lot of them and found them a bit too hot for my long-range .223 Rem 90gn VLD and Re15 / VarGet loads. They gave around 30-40 fps more in this cartridge than either the CCI-450 SRM or my favourite by far, the old PMC (Russian Murom) SRM which we can no longer get in the UK under any name. In fact getting any SRM or SR BR primer is virtually impossible here and has been for maybe 12 months.
