MIDI songs can come in handy in many different ways. MIDI files actually tell the player each individual note to play on each instrument. One could even think of MIDI songs in terms of sheet music; they give you the ability to switch out notes in songs in order to turn it into something completely new, or to recreate the entire song with different instruments and styles and so forth. In fact, with the right equipment and programs, you can even compose MIDI songs and then print them out into sheet music. Doing so is a great way to hear your composition before presenting it to people who plan to play it on live instruments.
The use of MIDI songs gives people a lot of versatility. For example, if you play an instrument, you can compose an entire song and allow it to run in the background while you play. In this manner, you are essentially playing with a band. If you don’t have any musicians to back you up, an MIDI of royalty free music will do just as well. No matter what instrument you need to support you, an MIDI can be made to imitate it and play the correct notes.
You can also get songs out of your head through the use of a MIDI sequencer and an instrument that allows you to put those notes into the program and compose the song. Many composers still do this today in order to get down music that they may or may not use later on. From there, music can be arranged and orchestrated into full pieces and translated into real instruments.
MIDI songs have plenty of use, provided you know how to make the most out of them, as well as have the correct software and instruments in order to do so.