Tony Maserati uses the Waves DeEsser to manage sibilance in backing vocals for better separation and to ensure they sit well behind the lead vocal.
By reducing the sibilance in the doubles, Maserati ensures that the lead vocal remains clear and prominent in the center of the mix, even when the backing vocals are panned to the sides.
This technique helps maintain a clean and focused lead vocal, preventing it from being overshadowed by the backing vocals, which can otherwise create a cluttered sound.
Maserati emphasizes that the ear doesn't need multiple sibilant sounds, and by controlling these, the mix achieves a more polished and defined sound.