The traditional, on-premise Clarity has been developed over 10 years. It has over 60 types of tasks and many features.
Clarity Cloud is a brand new product, so its feature set is more basic – but will grow quickly. Running tasks in the Autodesk Cloud has a number of significant restrictions today around Cloud Models, network access, and the ability to access addins (such as the Navisworks exporters), but these restrictions will also evolve over time.