There are definitely exceptions to this (generally correct) rule, in situations where performance does matter. RAM is still incredibly slow compared to the CPU

There are definitely exceptions to this (generally correct) rule, in situations where performance does matter. RAM is still incredibly slow compared to the CPU caches, so painstaking cache-optimization can make a huge difference when that's the bottleneck. Of course, if you're just writing some I/O bound program anyway, it hardly matters.