Personal preferences indeed
The reasoning for my liking of 25-27 m lines all the way down in kitesizes, and NOT using shorter lines with smaller kites:
Small kites (these are in my world below 6 m2 meaning wind from 15 knots and up) can be very on/off on a stupidly short depowerstroke, which dont feel good.
This evens out when using longer lines is my experience, as you use the window more efficient with a longer sweep, so feels a lot smoother now.
When we ride waves, or carve hard back and fourth - well, shorter lines wont speed this up, as with longer lines and small kites, you just pivotturn the kite on top while zig-zagging downwind - the same way we do on waveboards with small kites and lots of wind.
So you get a bigger windrange, a smoother ride, and carves/jibes are way better because the small kites that speeds from one side to the other much faster than bigger kites, has more time doing this now so feels like used to, especially if the wind is a bit down out there you also dont lack power in jibes.
If the wind picks up, you can fly the kite a tad higher all the way around your jibe/carve thus it is not slower like some suggest it would be.
Why not use even longer lines then ?
Because it starts to feel "saggy" eventually - eventhough to my surprise in lighter wind, when I have ridden a 12 m2 on 30 m lines for a while on a given lighter day, it feels natural and fast also if wind picks up, and very wrong when going down to 26 m again.
At first - as then you get used to it.
"Getting used to" is what it is all about here, where timing is not in our heads but our bodies.
Above is why I prefer lines from 25 to max 32 m, and never shorter, and in reality use 26 m (plus std bridles) for all sizes when wind, and longer only for the big ones when on the slow side
Some use their "normal" bar/lines from other boards out of convenience I know, others use shorter lines because they prefer these for their riding style.
I can never use the same kitesizes anyways, for waveboards and hydrofoils, way too much difference even if the wind changes a bit, so going from one board to the other makes no sense.
Got (at least but you know the principle) 3 bars with lines, 21 m for waveboards, 26 m for hydrofoil, 30-31 m for lightwind big kites hydrofoil. Never change bar length down when more wind.
"Using" extensions is a no no for me, riding so much that I dont want the hassle changing these, lazy, I know, but very convenient and easy
Would just try to put in words, why I like these linelengths - dont know if it can help (or just confuse) some