Not illustration - design (UI design, specifically). It's fantastic for maintaining styles/themes, collaborating, iconographic design, flows, and especially composable/configurable/modular UI components. The components are one of the standouts for me, as compared to other software. They are more powerful, and yet somehow less confusing/complex than in other software. In general, I always run into some kind of limitation or bug or confusing behavior in other software - Figma has by far given me the least trouble. They obviously have both enormously talented designers and enormously talented engineers in charge. Also, they appear to actually think about what the team-based UI design pipeline looks like in practice.

Edit: As others have pointed out, it's not so much the existence of a feature that's missing from other software - it's the design and implementation of features.

Edit: Their autolayout implementation is incredible. And their tutorial videos! My god, they're incredibly discoverable and informative and SHORT. I'm going to stop because I could keep coming back and adding edits to this comment all day.