Provisioned: Provision read (RCU) and write (WCU) capacity

needed per second

Dynamically adjustable (Unused capacity can be used in bursts)

Billed for the provisioned capacity whether its used or not

On Demand: Truly serverless and expensive

For unknown workloads or traffic with huge spikes

Use On Demand only when:

Workloads are really spiky causing low utilization of Provisioned Capacity OR

Usage is very low (for example, in test environments) making manual adjustments

expensive