Well, I don't use a phone app for it but I love doing vocal overdubs and choir versions. They usually happen when recording some guide vocals or the lead vocals track, even for songs or clips that don't really require any harmonies. Then my heavy Queen influence reminds me there are no songs that don't require any harmonies, as actually every song needs them, and more is definitely better.
Same for bands or projects. I'm always the one pushing for more vocal harmonies. Can't get enough of that stuff.
Greetings...
Nef