What is the point of a adafruit data logger
Are you referring to this?



That is a shield that has an SD card interface (with appropriate level-shifting for the SD card) plus a real-time clock.

The rest is "prototyping" area for you to install your own devices.


  In order to play an audio file, I was suggested to get an Adafruit data logger


I don't see how this helps play audio files, however you might read the audio file from the SD card. Then you need to send it to a DAC (digital-to-analog converter) to convert the digital information to analogue.

The Adafruit data logger is fine for recording data (for example, temperatures) but I don't see why someone would recommend it for playing audio files (apart from the SD card interface).


  my question is still, why data logger?


Better ask the person that recommended it, eh?