This is a great article and what @gdarchive writes is really important. I would like to complement the article because the stated is also true for orchestral music composition. Of course it's always up the to artist to decide how they want their piece to feel like. Imbalance is not by all means a bad thing, although it's usually what you would try to avoid. It's important, however, that the artist is aware of what techniques exist and what set of emotional experience they lead to for the listener. So, let's image, you got that really strong cello line which starts in the lower registers and then climbs all the way up to where the strings are almost screaming. Now your cellos are located in the front right of your orchestra. As said, we keep the tone but vary the color in our example here. So there're three things we would try to balance here: Texture, tone and direction. I will try to explain what each of them will do. And I will try to show why full balance is best in most cases but is not always what you want. So let's start with direction, or simply speaking "stereo". Of course, to balance a sound that comes from the right, we need to add one coming from the left. Be sure to not pick an instrument that isn't too much in the rear because this would lead to even more imbalance. A good choice would be a clarinet, maybe a bass clarinet or even the whole section of them. To keep our balance, we would have them play in their lower registers as well. Now we only have those low notes but maybe want to balance up to the higher octaves. Be sure, though, to keep them very silent as the high cello notes, that will come later, need to remain the strongest voice. As we are going for balance and don't what to set any counter voice right now, we need to carefully pick a matching color, something similar. Horns go very well with clarinets and would also get us some output from the rearer part of the orchestra. But maybe we want to swap the supporting colors to - again - gain more balance. Maybe the middle registers of the trombones would do when played piano in a very soft and fine tone. To accomplish the same sort of balance for the cellos we could use the bassoons but as we decided to swap the supporting parts, we might be going better with the lower registers of the violins. Remember, you can almost always intermix instruments of the same section together. We should now already have quite some balance in our piece. At least when it comes to color and direction. So let's go over to the texture. As of now, we only have a melody. The question we need to ask ourselves is: Do we want to support, complement or enforce the melody? Enforcing would mean that all the other instruments we have so far would either play pretty much the same the cellos do, or express a counter melody. This would give us a very powerful melody that is well defined and strong in its expression, no matter what the articulation tells. Complementing would mean that we try to fill all the pauses and silent notes the cellos play in their main melody. This would take away some rest but still establish some sort of balance in such a way that they would be alternating and taking turns, if you wish. Supporting the cellos would mean to let the other instruments almost play straight chords, either allowing the cellos to break out of them every now and then, or to re-harmonize everything the cellos do (which is harder to do but creates a softer and more fitting overall experience). I won't go too much into percussions here but remember that they also consist of very different colors and tonal heights. Use them as such! That is: Having very fast bass drums under very quick double basses will lead to nothing more but audio porridge while placing a few cymbals or triangle hits over the double basses will create interesting rhythmic patterns.