I don't think that's at all the main one given OP's list of apps. It'll accelerate things built in Apple's Swift/ObjC ecosystem, but it's not going to help node

I don't think that's at all the main one given OP's list of apps. It'll accelerate things built in Apple's Swift/ObjC ecosystem, but it's not going to help node, android, react native toolchain, etc. And regardless of that, the instructions speed the atomic operations required when updating references in a mulithreaded environment. It's lowering active CPU use. They're not going to do anything to reduce the impact of a mostly idle application in the background on the rest of the system. The reference counting mechanism itself does mean you don't have to walk memory as much to do garbage collection, which risks pulling rarely used memory back in from swap. But that was true on the Intel Macs, too.