> It's not just the storage itself (which is really cheap nowadays), but more of the fact that every byte read and written needs to go through the processor, pollutes RAM and poisons caches. Less storage usually translates into direct performance gains as well.

FWIW, I think that's currently a good chunk away from being a significant bottleneck in postgres' query processing. But we're chipping away at the bigger ones, so we'll probably get there at some point.