[SJC_Hacker]

A bunch of smaller distributed instances could be cheaper than one big one at equivalent size/compute. It also allows you to grow as needed, without worrying about things like DB transfer, instead of absorbing a big upfront cost.

I agree it adds alot of complexity to the problem, which is another cost.

I guess this would be another argument for pay-as-you go cloud-managed DBs, despite being more expensive than rolling your own.