Maintaining compatibility across various systems, programs, etc. is generally a good idea, as to allow it to be read across various platforms. For instance, a PDF can be read on a very wide variety of platforms and programs which run on those various operating systems and architectures (Windows, Mac OS, Linux, Android, iOS, etc.), allowing a plethora of people to be able to read it. On the other hand, a document which may require special software to open will not be able to be as easily read by so many systems, and henceforth people.
Hope this helps!
