Let me try again. Preload sets the ride height of the bike. It also sets the "starting point" for the suspension.
Let's look at the 10% / 30% numbers. This is a recommendation found in many preload setting procedures. The difference between 10% and 30% is 20%. Wherever you start, if your springs are right you will get a change between static and total sag of around 20% of total travel. With the SV that's around 25mm. Remember, the DIFFERENCE between static and total sag should be around 20% of total suspension travel if the spring rate is right.
So suppose you want to start at 25mm (about 20% of total travel) static sag. If your springs are about right for your weight then your total sag should be about 25mm additional, or 50mm total sag. Suppose you measure the difference between static and total sag on your bike and it comes out anywhere from 20% to 30%. Would you change springs? I wouldn't. That's close enough.
Let's suppose your bike shows 25mm static and 50mm total sag. Streets you ride are pretty bad and you're topping out frequently. You take some preload out so you now have 35mm static sag. What's your total sag? Answer: 60mm.
Suppose you are racing and you find under heavy braking you are bottoming out. You crank in more preload so your static sag is 10mm. What's your total sag? Answer: 35mm.
The 25mm sag due to rider weight will stay the same with those springs. Changing preload does not change the spring rate.
Also, some people prefer softer springs, some prefer stiffer springs, no matter what the numbers say. There's a good bit of personal preference involved. Starting guides are just that, starting guides. With experience riders zero in on what fits them best.