Biggest reason for macros, imo is situationally available abilities. I.e. the trooper shot that's only up when the target is disabled. Would be nice to prioritize that without staring at your cast bar for it to light up. And yes, the executes. Target at 50% health, obviously unavailable... But down around 40%, you start either wasting gcds waiting for execute to be ready... Or spamming other abilities and only having a chance to execute when the target is down to 15% health and there's no point using it over another skill that would likely finish off the target. Essentially, less time staring at your action bars, waiting for reflex abilities is a good thing.