Parallel can also be used during recording to get a better performance from your vocalist. It can make the sound of the voice huge.
Giving your vocalist a separate parallel signal in their headphones will make their voice sound produced and can often give them more confidence when recording. It gets great results because the vocalist feels like he’s singing on a record, not a demo without compromising the quality of your recording.
Read more about this here: https://www.audio-issues.com/recording-tips/use-parallel-processing-recording-get-great-vocal-performance/