In complex applications the $rootScope digest cycle can take a considerable amount of time. The ui-layout triggers a $rootScope digest cycle on every mouseUp (always) and mouseMove (during resizing) thus slowing down the whole application. This effect accumulates when multiple ui-layouts are used within a view, causing multiple digest cycles.

I have tried to simulate this issue in a plunker, by emulating a long digest cycle: Clicking on the button will open the alert with a considerable delay and moving the splitbar is very laggy.