Your app won't benefit from incremental GC during an event loop turn, because nothing your script did before the incremental GC slice will be made visible to users until the entire event loop turn is finished.
But what about the all the other processes in the device? There may be another process at the same time who may benefit from such GC, perhaps a video being played inside a plugin, or just Photoshop being run side-to-side with the browser and things like that.
It may not benefit the app but it may benefit the user, which is clearly a relevant metric.
It may not benefit the app but it may benefit the user, which is clearly a relevant metric.