Could anyone give me some user scenario(s) where the new scale function is usable? I understand how it works but I haven’t quite understood its purpose yet.
Are you talking about the instrument muscal scale scaling?
Not only, it is also usable for some serious purposes.
For example, imagine your song is playing in C major scale, meaning, the notes that you are allowed to use are only CDEFGAB. You can’t use sharps, like C#, D#, and so on.
Now, imagine you have a phrase that plays CEG (first chord, basically), which is the I, III, and V notes of a given scale. Let’s try to see, what is going to happen if we shift the chord by exactly 2 semitones: DF#A (D major). While it does not seem that there is anything wrong with this chord, this does not belong to the C major scale anymore as F# note is not used in it, it is only the white keys that tone is allowed to use, or more precisely II, IV, VI notes of the scale, which are DFA (D minor).
If you set the instrument to this scale, it will be shifted to the right chords automatically. On the side note, I personally think it would make more sense to have the selection of the scale global, instead of having to manually set it for each instrument individually, but it will work this way too.
And in that respect it might be nice to have a selection for scale song-wide, or something.
kind of a tool for someone who constructs his music scientifically and still needs the tool, a wizard that assist him 
(nah i do get it, you’ll save the work of a few scale corrections, but for the price of knowing nomenclature and algorithmic rules, which is why i’ll stay away of it, i’m dumb, i want just notes)
It’s also useful as a chord tool.
For example, create a phrase that is only one line with looping disabled. Enter the notes you want in your chord across the phrase tracks and map the phrase across the keyboard. Now you can play chords with single notes, you can develop this further by having different chords in each octave etc…
Not sure about this as it’s nice to go outside of a scale too. Maybe this function can be coded as a tool… Something like make all instruments the same scale as the selected instrument…Also while on the subject it would be nice to be able bypass the scale per instrument via player command.
I see some other potential uses for this feature.
Doubtless, many of those here are quite desperate to learn to play keyboard, but when one looks into what it entails, most choose not to, simply because there is way too much practice involved. Like, 12 different root keys multiplied by at least 2 or 3 scales. That involves a lot of practicing, not many would be able to devote that much time in adult years.
But instead one might get away by simply learning just one scale: C major, which is incidentally the easiest to play, since it is basically just the white keys of the keyboard. After one has learned the scale real well (which should be magnitudes less work than to learn like 36), one can play pretty much any melody in any key by simply setting up the scale of the instrument in the sequencer and the key offset in the MIDI keyboard.
By the way, one does have to leave the scale sometimes: such notes are called accidentals, and we indeed may need a way to allow for them.
That would be nice in some sense, but if you design three or four different arpeggio schemes that you really want to bind to a specific scale, then the global scale would be in your way in that regard.
The scaling mode does allow you to keep the amount of required instruments for arpeggio schemes as low as possible.
The scaling thing seems to fit nicely for chord progressions overall, when one has a bunch of one line chords recorded as phrases that get shifted nicely along the scale with very little effort by simply specifying the root note.
It does not seem to me that it makes much sense to have scaling enabled for melodic phrases as it would break some intervals during shifting in a specific scale.