In short, ADR is (automatic dialogue replacement). It is an audio post-production process. Thus, they practical use in movies. Specifically, re-recording in studio the previously poor audio quality speeches. Afterwards replacing them with desired results. For this reason, the recording sessions are performed by the same actors that play in the film. However, often the film director is also involved in recording sessions. In particular, to bring the situation as close as possible to that scene in the movie. For instance, not to lose any dramaturgy within just a dry studio voice recording process.
Film Sound Berlin