HDFS file formats
There are multiple formats in which you can store a file in HDFS. For example, HDFS can be used to store images in GIF format, text data in plain-text CSV format, or spreadsheets in XLS format. This is similar to how you store files on your computer's local filesystem. A storage format gives indications to the underlying storage system as to how the file should be stored. This is usually indicated by the extension of the file.
Although one may not realize, choosing the right file format for your data is important to get the desirable performance from your big data storage. [5]—https://community.hitachivantara.com/community/products-and-solutions/pentaho/blog/2017/11/07/hadoop-file-formats-its-not-just-csv-anymore.
Some of us may confuse file formatting with flexible formatting. You may ask that the basic idea of Hadoop was to be able to store format-free data, also called unstructured data. Then, what is the need to have a file format in the first place? The question is valid...