Bigger ASM means you can fit less code in cache, which makes your code slower. If this happens in a hot loop, it may be the difference between "my code fits ent

Bigger ASM means you can fit less code in cache, which makes your code slower. If this happens in a hot loop, it may be the difference between "my code fits entirely in L1 cache" and "my code needs to be fetched from L2/L3". This matters in high-performance scenarios. The fact that you can introduce a performance issue simply by creating a temporary is absolutely bonkers, and makes writing high-performance code more complicated than it needs to be (and god knows it's already very complicated).