As a listener and not a user of any Vocal Synths, I find my favorite covers have a good amount of variety in how the vocals are tuned through most of the song. Extremely excessive tuning can be extremely good in an emotional finale before the music closes out, but every vocal has their limits. If you have a 10/10 throughout the whole song, it makes the emotional climax either feel the same as the rest of the song or way too janky when trying to push for an 11/10. It genuinely depends on the song where to use vocals with nothing changed, vocals that have some work done on them and vocals where you just went ham on every option for a section.
In the end though, thats just my opinion. I think what sounds good to you is ultimately what matters at the end of the day. The driving force in Vocal Synth producers and cover-artists having different and unique styles is how they look at their work and go "Yeah, thats pretty good!" Pick out some traits you like in other songs and covers that use the vocalist you're using. See how you can replicate that general sound in the program for practice (ask others for help if you're stuck), and see if what you learned can apply to any covers you plan on doing!
