Since these are the same file format, SSIS doesn’t have to parse or translate the data between the data streams or the raw file format. This results in the raw file format being faster than most other data source and destination formats. For some statistics on the speed benefit see this post by John Welch (blog | @John_Welch).
The raw file format can be incredibly useful. It can be used for either a data source or a data destination. Once you’ve gotten your hands wet with them, you’ll find a great many uses. Some of which may solve issues that you’ve run into with previous development projects.
For instance if you want to build an SSIS package that processes data in multiple steps, temporary versions of the data can be stored in raw files and passed between data flows. This will allow packages to be built such that they can be restarted at different points in the data processing.