Using Playlists for Parallel Processing
One of the uses of playlists is to apply multiple effects to the same
audio stream. For example, let's say you would like to apply two
different non-linear effects such as distortion or compression to the
same audio source (for linear effects, you could just apply them one after
the other in the same track).
Create a new track, apply the original track's playlist, and then apply effects to both tracks independently.
The same result could be achieved by feeding your 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"
Using Playlists for takes is a good solution if you are going to need the ability to edit individual takes, and select between them.
Each time you start a new take, create a new playlist with p > New Later, you can Select your way back to previous or later takes as desired.
If you want to create a composite edit from multiple takes, create a new
track to assemble the final version, and "cherry pick" from the playlists
in the original track by copying regions over as required.
Alternatively, record each successive take on top of the others in "layers" and then edit them using the layer tools, explained later.
Using Playlists for Multi-Language Productions
The same approach as for takes is useful when you are recording or
editing content in multiple versions, such as dubbed movie dialog in
several languages, and you want all versions on the same track, to
get the same processing.
Select the appropriate language before exporting the session.