Lurssen Mastering's engineers explain why a high-frequency limiter sits after EQ in their mastering chain, and why they think of it as something other than a de-esser. The tool actually engages from around 2.5 kHz, working through the upper mids, not just the air frequencies most people assume.
The core idea is about translation. When a mix comes in too dark, often because the mixing engineer was working on speakers that exaggerated the high end, mastering needs to add a lot of brightness. Push too much EQ into a dark mix without any control, and you get harshness, brittleness, and that digital edge.
Placing the high-frequency limiter after the EQ lets you brighten aggressively into something that catches and smooths the excess. The result feels open rather than sharp. You can push both processes hard against each other, or apply just a small amount of each, and either way land somewhere that sounds like nothing much was done at all.