These are just the means of recording audio that I have personally used over the years. Of course there are many more alternatives...
The point of this is that recording music these days is incredibly easy. So easy that much of what is heard in current popular music can be created readily in the home studio, bedroom or garage (read my blog post on AutoTune for more on that). The process of getting a composition idea from your head and into a recorded form is child's play.
But what is the longevity of these recordings? I have many cassettes of original music I recorded only 15 years ago. I have 6 stereos in my home and none have a working cassette player. But I don't need one - I stopped listening to music on cassette years ago.
So what of the music I recorded on that format? Some of it I have continued to perform over the years and could still sit at a piano and play now. Other pieces I vaguely recall while several more songs and song ideas have been lost to time.
From cassette, to CD, to mp3 - the times will continue to change. The next generation of digital formats are just around the corner. Then what will become of all the music currently committed to mp3 or CD? Will that music's fate be the same as my old cassette recordings?
Music notation - sheet music - however, is a relative constant. The same music written hundreds of years ago, well before any form of audio recording was developed to capture the performance, could be performed today from sheet music.
As well as longevity, sheet music has an additional benefit. Many people long to read a great story in a book rather than be presented the story in film, allowing their imaginations to conjure the scene, characters' faces and surroundings. Music notation allows the performer to add his or her own interpretation to the music. This allows the music to truly live.
After a recent request from a client to provide piano notation for his wife as an anniversary gift, I have a renewed commitment to score all of my own compositions.
One day my great grandchildren may pick up a box of old things and with a puzzled look cast aside cassettes, CDs and mp3 players - but I can image a feeling of pride when they see an ancestors' name printed at the top of some sheet music. They'll just need to find a musician to perform it...