In my experience dialogue bubbles have always have a knack for polluting the screen, one, two or three you probably won't notice it, but when you see 30 overlapping over one another while trying to read the one that is under all of that have always been a cause of irritation for me, also bubbles would be more sprites that a computer would need to relocate resources too, I mean yeah some might have a kick ass computer that could deal with it, but not all.