MIDI Loops are kind of similar to a Track Preset, but not only does it save all the information that a Track Preset does (Instrument, Inserts, Strip, EQ, etc…) it also saves your MIDI notes and controller (CC) data too! Plus it can also do more cool things like link playback in Media Bay to your Chord Track! MIDI Loops let you easily reuse instrument patterns you really like in other projects, for example: say you made some epic chords but they don’t quite fit the project you’re working on? Save them as a MIDI Loop to use in a future project! Or, say you created a really cool uplifter effect which you would like to use in future projects but don’t want to save it as an audio file because it might not match your future projects key just save it as a MIDI Loop! You can even create MIDI Loop sessions where you experiment with different melodies/chord progressions, effects, drums, etc… and save the good ones as MIDI Loops to use in future projects.
http://www.cubasetutorial.net/2013/08/13/how-to-get-the-most-out-of-cubases-midi-loops/