@ASG:
While there are other members who can explain it better than I, I'll try.
First, I'm gonna start with midi. You know about channels, right? While they aren't the same thing, if you're starting out you probably co-sign channels according to the track's number. (Ch1/Trk1, etc.) Even if you've een at it for awhile, it avoids confusion - that is, until to start moving tracks around; however, track =/= channel)
If a sound is duplicated (same sound + channel), the sound gets boosted drastically. Now, unless you want this, avoid this. If you run out of channels, bounce the midi to audio to free up more channels - although the same 16 are available.
Now, with the midi volume boost out of the way:
Stereo Separation which you can get with audio tracks easier than midi (if that can be done with midi, idk)
While midi has the volume boost issue, audio has a phase issue. This can be demonstration if two people singing/talking into mics pass by each other. The audio heard from the speakers goes silent momentarily.
This is due to the "sweet spot" where the mics cross and the audio may die down before it completely stop. This is known as "phase cancellation." Dance/Techno genres use this sound predominately.
Think of it like "crossfading," but what's suppose to "fade-in/out" does so too late.
This is the case when two or more audio tracks collide/coincide with each other. They're both fighting for that "sweet spot."
The best example I can think of is an airy vocal recording doubled. There's going to be some phase there - possibly an egregious amount if it's not tamed well. Now, you may not get the phase, but like you said, you don't want some tracks sitting on top of each other.
Therefore, nudge one of them ever so slightly and this adverb is key if you want to to appear like the whole "Stereo Field" (where pan comes in) is being used.
Relating this to midi. Regarding the piano + strings in my tracks, neither are strictly on beat. (This is just with straight chords, but my bass lines are certainly off-beat/syncopated very often)
It's common for the piano + strings to be layered, doing the same thing at the exact same time. However, "nudging" one or both gives them the "separation" to help maintain their separate identities even if they seem like they're doing the same thing. (ie: either one is on beat while the other is slightly off.)
With me, everything besides the rhythm is off-beat and perhaps it's also off-beat; however, in complete context, it all sounds very well glued together
Again, that is "Stereo Separation" for midi.
It's the same with audio.
Let's say you have Vox 1 and 2 60% from center equally to get better separation, so it's the same thing, but done at a different time,
slightly nudge one of them by a few ticks. This "widens" the signal across the stereo field. I recommend this because subtly is one's best weapon. It'll take practice, but this can be achieved.
An example would be layered instruments. Unless you want to be obvious:
This is a PIANO + STRINGS; however, when in context and even not - This is PIANO + strings is probably better. Heard than seen or Seen than heard. With me so far?
With vocals (but not limited to), this technique is used adamantly. It's obvious we can tell the panning situation: Lead Vocal center, BGV away from center, but they aren't completing with the lead vocal. Whether they're all singing the melody or the BGV consists of complex harmonies, the lead is dead center because it is the most important part.
Much like principle instruments in the orchestra. Where to they sit? Upfront and center because they lead the entire group! Now, members are surrounding them whever the section sits, but they are the focal point.
LCR panning is just one part of stereo separation, but timing is the other part.
Off-beat bass + strings surround the on-beat piano.
Off-beat everything else surrounds the on beat drums. Try listening to something syncopated without rhythm - and no matter how well you can count, you'll miss a beat at some point. (Unless you know the song top to bottom, back-to-front and sideways)
Techno/Dance and everything in-between those two genres are famous for syncopation tripping you up until the beat comes in.
This ties in as the nudge vocal is "off-beat", though you can't tell because of how subtle or because everything else is playing.
I gave the example of the Chorus effect. It's many instances of the same sound (signal) that is slightly off with each instance. This veers into frequency/frequency of pitch, but:
A440 doesn't sound like A440 when the chorus knob is wide open; however, as you slightly creep it upwards, you start to notice the effect. The note becomes "fat or widened" because of all the "wet" signals diluting the dry one. (Reverb/Delay/Flange/Phase works the same way)
If you're still confused, play with those "wet" knobs to see how they function. They're just "quantifying" the repeated signal.
Did this help as well or no? I did touch on other issues, but they do tie into this. (I think)