When interacting with different services or program there often comes the point where some sort of file has to be parsed into a data structure, which can be processed later. For standard file formats like XML or JSON parsers are available for almost any language out there. (BTW I love the graphical representation of the JSON syntax on their website.)
There are however situations in which one has to deal with a proprietary file format or with vendor-specific extensions to a standardized format. At this point a parser has to be written. It seems a boring task, however there are several important aspects of programming which can be learned here.