It's great for performance, up until you reach the point where a single device becomes a bottleneck, at which point it's terrible for performance.
As a sibling comment says, you ideally want to shard on some other key to get "just enough" distribution that all your machines/disks have work to do, but you are still only hitting a limited number of hot sectors on each disk that can be effectively cached. But that requires active monitoring and rebalancing of your data as it grows. Totally random keys are a safe default that will scale with any kind of data distribution and access patterns.
As a sibling comment says, you ideally want to shard on some other key to get "just enough" distribution that all your machines/disks have work to do, but you are still only hitting a limited number of hot sectors on each disk that can be effectively cached. But that requires active monitoring and rebalancing of your data as it grows. Totally random keys are a safe default that will scale with any kind of data distribution and access patterns.