One of the uses of playlists is to apply multiple effects to the same audio stream. For example, applying two different non-linear effects such as distortion or compression to the same audio source (linear effects can be just applied one after the other in the same track) can be done by creating a new track, applying the original track's playlist, and then applying effects to both tracks independently.
The same result could be achieved by feeding the track to multiple busses which then contain the processing, but this increases the overall latency, complicates routing and uses more space in the Mixer window.
Using Playlists for takes is a good solution when one needs the ability to edit individual takes, and select between them.
Each time a new take is started, a new playlist should be created with p > New. Thus, later, any previous or later takes can be selected as desired.
Creating a composite edit from multiple takes, can be achieved either:
The same approach as for takes is useful when recording or editing content in multiple versions, such as dubbed movie dialog in several languages: having all versions on the same track allows to apply the same processing, making it easy to switch language before exporting the session.