Q: how do you decide what sentences/words need to be gradually revealed or "spoken" in the speech bubbles and which can just be fully visible at the moment the speech bubble appears?
A: if the phrase is unique, especially near the end, then 'word pops' (individual words revealed one at a time) are more appropriate, so that the more unexpected words have an impact. but when it's a phrase that's more predictable, it's usually better shown all at once