The direct control of the Peripheral's registers is a low-level way of creating peripheral driver which requires a good knowledge of the target platform and the code is typically not portable to different platform. However, in some cases is this method more effective or even necessary to use (in the case of special chip features not encapsulated within the Embedded component implementation). See Low-level access to peripherals topic for details.
The common basic peripheral operations are encapsulated by the PESL library commands which is effectively implemented using the simple control register writes. See Processor Expert system library topic for details.