You get direct connections to the servers without going through multiple local jumps and you aren't slowed down by the slower speeds of light in fiber.
Error correction, mass limits, and power generation are the difficult parts.
* Ping time would be roughly 1 hour
* Would require high-power wireless communication link
* Would take over 1 year to ship new hardware to datacenter
* No magnetosphere means increased hardware failure due to radiation.
I wish I knew the math to calculate how much energy would be needed to send data to Ceres and back, because I think the transmission energy might be large enough that it would prevent the cold-storage use case. Reading and writing from flash storage probably requires less energy. That means this Ceres data center would be best suited towards low data, high computation, latency is irrelevant computation. Maybe brute forcing encryption keys or advanced fluid dynamics modeling.
[0] Ceres is 50% water by volume.
Or are fission byproducts just that low energy when it comes to flipping bits?