It seems like a lot of these "rules" for systems were created decades ago with different hardware. Not only has the hardware design changed since then, but the

It seems like a lot of these "rules" for systems were created decades ago with different hardware. Not only has the hardware design changed since then, but the economics have changed as well. With a single big-iron mainframe it probably made sense to spend a lot of money on cooling because any failure was very expensive. With many commodity servers it may be cheaper to let them run hotter and replace any failures, though an Intel study with free-air cooling in Mexico found no significant difference in failure rate. I'm reminded of hot-spares in RAID configurations. With today's hard drive sizes it can take so long to merge a hot spare into a system that you're better off just increasing the raid level and only having online drives.