Please note that the following information is based upon my own limited understanding of the subject and may be inaccurate. If you have access to a music teacher or similar, they may be able to explain the subject more completely. Since writing this post, I've learned more about this subject from the excellent Coursera course "Write Like Mozart: An Introduction to Classical Music Composition". If I get time I'll revise and add more detail (perhaps in a 2nd part). Wikipedia defines voice leading as follows
I was taught to use voice leading to smooth the transitions between chords, so that the chord can be separated out into smooth “voices” which can be then used as the basis for individual instruments.
Say you have a I IV V progression in C Major. Looking at that visually (in MIDI in this case), you can see that there are quite big movements between the chords (i.e. C –F – G).