Comment by piker

It's a great question and primarily for the snappiness, but in the end there isn't much difference since the heavy stuff (shaping, layout, rasterizing, etc.) is cached anyway. It's inspired by Zed which also has an obsessive (disciplining) focus on FPS.

Technically, using immediate mode avoids a ton of callbacks/listeners or something else which allows for hundreds of docs to be held in memory usefully without hogging resources. That's an actual use case for this.