Same colour, different question
RGB answers "how much of each light". HSL answers "which colour, how strong, how bright". Both describe the same point; only one of them lets you move it deliberately.
If you have channels from a canvas, an image sample or an API and you want to build a scale around that colour, this is the step that makes it possible.
Building a scale
Once you have hsl(11, 100%, 60%), a usable ramp is the same hue at different
lightness — 90%, 80%, 70% and so on. Keep saturation slightly lower at the light
end and slightly higher at the dark end, or the pale steps look washed out and
the dark ones look muddy.
Rounding
Degrees and percents are whole numbers here. Converting back to RGB can land one value away from where you started; that is the cost of a form humans can read.
Questions
When do I need this?+
When you have channels — from a canvas, an image sample or an API — and you want to build a scale or adjust the colour deliberately rather than by trial.
How do I make a good scale from it?+
Keep the hue, vary the lightness, and let saturation drop slightly at the light end and rise at the dark end. Equal steps of lightness alone tend to look washed out at the top.
Is it lossless?+
No. Degrees and percents are whole numbers here, so converting back can move a channel by one.