Well, well, well - there was a qualifier …. Memory does not grow on trees. Memory Costs Money!!!
Meaning.... if you have a 5000 sq ft house, do you reserve and luck up 1-2 rooms just in case, you don't run out of usable space? No! …. when you reserve "some" memory to the O/S (more memory than it actually uses), that means SQL server is deprived from unused memory that can be used all the time.
I can guarantee, 75% of the instances around the world is has 0 as setting, because it is "default". Do you think Microsoft would allow such wide-spread performance problem exist?
If you reserve X amount of memory generously, what percentage of the (even Prod) servers were monitored closely as O/S requires a bit more memory over time.... (ie. new services, security and monitoring toss added over time).
When people say, there will be Perf issues.... what does that even mean? 1%, 99%, temporary, forever until a reboot? Imagine all servers with Memory Setting = 0, has to be restarted once a week, every day. Just does not make sense for so many reasons!
Do we really think, Microsoft would be so stupid to allow O/S starve for Memory?
Additionally, regardless of the memory settings (generous or otherwise), when you look at each server's trace logs (regardless how much memory is reserved for Windows) you will see plenty of events happening "all the time"... RESOURCE_MEM_STEADY, RESOURCE_MEMPHYSICAL_LOW, RESOURCE_MEMPHYSICAL_LOW
What do you think, Microsoft is not capable of setting the memory-starvation threshold to ahead of what the Server needs?
I think, this idea of O/S starving for memory is an outdated myth (from NT days) that is no longer valid since Microsoft had years to perfect this memory exchange and I believe it is working perfectly for the last 15 years at least.