Pro Great sheet sharing web page
So you composed a new score! Now what? Well, you can start by putting it on the muse score sheet music sharing web page where others will be able to enjoy it and comment on it. Or maybe you're just looking for a score from an old video game: in that case, you should probably search the page for it, and download one of the many available formats (pdf, muse score format, mp3, xml, etc).
Pro MusicXML import and export ensures a degree of compatibility with other programs
If you are submitting files to a publisher, MusicXML format can be read by the big engraving programs: Sibelius, Finale, MuseScore, etc. Often there are some display issues that will need to be tweaked when using MusicXML between different programs, but publishers will spend a lot of time tweaking the file anyhow.