There are endless MIDI files on the net. Here's what to keep in mind about MIDI when looking for free printable sheet music...

Is MIDI (Musical Instrument Digital Interface) a good format for free printable sheet music?

MIDI's primary purpose is to record musical performance, NOT for musical notation. However, MIDI can be used for notation purposes, although somewhat disadvantaged for this use. For example, there is no support for notation like staccato, crecendo, repeats, etc. in MIDI. But MIDI can "record" a musical performance very nicely.

MIDI files can be created in 2 ways: recorded from a musical performance (like a digital keyboard), or output from musical notation software. Here is my MIDI keyboard (Roland RD-600 digital piano):

Music notation software generally has the ability to output MIDI (for playback purposes). Music played back via MIDI from music notation software will sound mechanical, as if played by a robot. This is because the notation software will make an exact conversion of the notes with exact timings. This "exactness" sounds mechanical, not human.

Here is my "old-fashioned" MIDI sequencer. It acts as a "tape recorder" to record output from a MIDI device (like my MIDI keyboard):

MIDI allows for recording with an arbitrary MIDI device (most commonly a keyboard), and allows playback in any number of voices. This is how digital keyboards and synthesizers allow for playback in different with differnt "voices" (sounds). Here's part of the control panel on a digital keyboard which allow for selection of different sounds.

When a person performs music, it is the "inexactness" and varation that makes the music sound human. It is in the "inexactness" that emotion and feeling are added to the performance. It is the minute (and non-minute) variances in volume and tempo that make the virtuouso's performance...virtuouso. When looking for free printable sheet music, you are want exactness, as the sheet music is intended ro show.

The mechanical MIDI playback of a music file is helpful to "proofread" a music notation file (to make sure that you have the notes and timings correct). It is not meant to be pleasant to listen to. Because of the mechanical nature of exact MIDI playback, some musical notation software has "humanizing" features that will make MIDI playback sound more "human". "Humanizing" features try to mimic some of the characteristics of human performance. But "humanizing" is still a far cry from reporducing the variation of a skilled musician.

In contrast to MIDI generated from music notation software, a MIDI file that was created by recording a musical performance (like a digital keyboard, or digital drums) can sound very close to the actual peformance. There are MIDI voices (instrument sounds) for just about every type of musical instrument imaginable. Some types of instruments sound more realistic than others in MIDI. In general the more "percussion like" an instrument, the better it will be represented through a MIDI recording. Performances by keyboard instruments, drums, and the xylaphone can be well represented quite well with MIDI. And violin, tuba, and cello performances would not be represented very well via MIDI.

The main thing to keep in mind about MIDI files (for the purpose of free printable sheet music) generated by "recording" (sequencing) a musical performance is that it does not translate well into a piece of sheet music. The popular music notation programs have the ability to take input from a MIDI file or device. However, due to the "inexactness" or variances of a real performance, these MIDI sequences are not very easily translated into sheet music in notation software. There are much better formats available for printable free printable sheet music.