Small systems are good for realtime applications. Then the resources for an application have to be ready all the time. In terms of space/power/reliability/scal

Small systems are good for realtime applications. Then the resources for an application have to be ready all the time. In terms of space/power/reliability/scalability large systems win. Sure a single raspberry doesn't draw much power. But it doesn't provide much computing power either. Throw in a few hundred of those systems and you feel the heat. Still the computing power is comparable to a single rack server. You want to use a RAID6 on the raspberry, sure, can be done but throw in 4 times the number storage devices. Compare that to the rack server with 16 SSDs configured as RAID6 where the data is shared by hundreds of virtual machines. If you compare the "energy per bit" or "energy per operation" the high-powered server CPUs win versus most anything out there. So I'd say: * If you can justify a real server, do use one instead of dozens of "simple machines". * If you can use the cloud do it instead of providing your own hardware. * Exceptions may apply where security or reliability is concerned. (You wouldn't run your heart monitor in the cloud when a small dedicated system does the job.)