TSimpleDataSet is intended for use in a simple two-tiered database applications and briefcase model applications. It provides an easy-to-set up component for linking to the database server, fetching data, caching updates, and applying them back to the server. It can be used in most two-tiered applications. 

There are times, however, when it is more appropriate to use TClientDataSet:

• If you are not using data from a database server (for example, if you are using a dedicated file on disk), then TClientDataSet has the advantage of less overhead.
• Only TClientDataSet can be used in a multi-tiered database application . Thus, if you are writing a multi-tiered application, or if you intend to scale up to a multi-tiered application eventually, you should use TClientDataSet with an external provider and source dataset.
• Because the source dataset is internal to the simple dataset component, you can't link two source datasets in a master/detail relationship to obtain nested detail sets. (You can, however, link two simple datasets into a master/detail relationship.)
• The simple dataset does not surface any of the events or properties that occur on its internal dataset provider. However, in most cases, these events are used in multi-tiered applications, and are not needed for two-tiered applications.