>If hogging lots of RAM makes my program legitimately run better

It objectively doesn't make your program run better to waste RAM.

If RAM usage goes up 2x every two years but RAM and hard drive speed go up 20% in the same time period, then using more RAM when you don't need it is making programs more sluggish to start and to suspend to disk, and it's making computers draw more power while sleeping (to keep that much RAM alive -- the D in DRAM means every bit in the RAM needs to be refreshed continuously).