HSL saturation is a mathematical property, not a perceptual one. Two colors with the same HSL saturation value (e.g., 80%) can appear dramatically different in perceived colorfulness if they have different hues or lightness values. Yellow at S:80% appears extremely vivid; blue-violet at S:80% at the same lightness appears only moderately vivid. This discrepancy exists because the HSL model was designed for computational simplicity, not perceptual accuracy. Perceptual chroma — the measure of colorfulness that matches human perception — varies significantly by hue even at constant HSL saturation. Working in HSL gives you mathematical consistency but perceptual inconsistency; working in OKLCH gives you perceptual consistency at the cost of some computational complexity.
The practical consequence of uneven perceptual chroma across hues: a palette built in HSL with consistent saturation values will look unbalanced. Yellow entries will look more vivid than blue entries; green entries will look different again. If you are building a categorical data visualization palette or a brand color system where each color should feel equally prominent, equalizing HSL saturation is not enough — you must equalize perceptual chroma. The OKLCH color model provides a C (chroma) channel where equal values produce equal perceived colorfulness across all hues. Tools like oklch.com and modern CSS color functions allow you to specify colors in OKLCH and get perceptually balanced sets.
High-saturation palettes are harder to work with than low-saturation palettes for most UI design contexts. Highly saturated colors create strong simultaneous contrast effects at boundaries (the borders between colors appear to glow or vibrate), which increases visual noise and reduces readability. They also have less room to maneuver for hover states, active states, and selected states — adding saturation or darkening a highly saturated color quickly produces muddy or clashing results. Low-to-medium saturation palettes give you more room to create state variations and are easier to use in large surface areas without creating eye strain. Reserve high saturation for small accent elements, data visualization, and deliberate high-energy design contexts.