Originally Posted by SeijiSensei
The last show I watched where the actors' performances were recorded before the animation was done was Kurenai. You can see how effective this is in episode three where there is a frantic three-way conversation. It adds a lot of realism since we know that, in real life, people do not patiently wait for someone to finish speaking before speaking themselves. In that Kurenai episode, the director encouraged the actors to talk over each other and left the animators to work out how to translate that to the screen. I suspect there was some ad-libbing as well.
I also remember Red Garden
, the 2006 anime that had used the same technique with great success as well. Like you mentioned, it is a good method to add realism to a scene, especially if it is of an urgent nature and the characters (or rather, the actors) frantic speech and tone could really sell you on a scene in a way that a more carefully calculated script wouldn't have done.
Of course, I could imagine why such methods are normally not used, since they depend greatly on how talented the Seiyuu involved are and how good the chemistry between the cast is, otherwise it could end up with a very mixed result. That and ironically, since anime dialogue is scripted, having natural sounding dialogue might come across as being odd.
Regarding lip animation, as mentioned, it would cost a lot of money for something that mundane, not usually very noticeable and can go by so quick, so it wouldn't make much sense to spend that much effort into that area when they could manage their creative force on other more noticeable areas.
That said, the fact that there is little focus on animating lips can actually give scenes where they do focus on a character mouth even greater impact. I remember Pandora Hearts
trying to pull that off once when an important character made his debut, where once he said his name the camera shifted focus to his lips and we seen a very quick but fluid animation that managed to give the scene importance and ended the episode on an exciting cliffhanger. Recently, Shin Sekai Yori
had done something to that effect as well but rather for a more ominous effect, with a character silently mouthing a word.
It could be argued that the camera work is more important in such cases, but in a way, I don't think that those scenes could be as potent if the entire show had the same level of animation when it came to that particular area. There is also cases where lips animation can be used effectively in an anime opening and endings, where a character might sing the same verse as the singer of the theme, and that could give off a very strong impression as well if done correctly (Off the top of my head, Bleach
had used this twice at least, and Fullmetal Alchemist
had done it in it's first opening).
And that is only on that area, if someone gets really creative with it and could manage to make the lack of animation into a strength by juxtapositioning it with a few moments of importance in the show where the animation quality is upped, and that emphasis the importance of the scene.