Imagine a data file with data (a movie, an image, etc.). A file is just a sequence of 1 and 0. Since Pi contains infinite many binary digits, that image should be found in Pi somewhere and instead of sending someone a file, we could just send them the offset to that file in Pi.
The problem with this approach (ignoring the implementation details) is that the offset could be larger than the file itself, meaning that the offset can be longer than the file itself.
However for some files (or parts of file) it's possible to instead send the index in Pi instead of the file data itself.
What is the biggest space save that can be reached by using index in Pi instead of the data itself for saving a arbitrary file?