There are people in this world who can walk in and nail a take with little or no preparation. I am not one of them. Nor do I know any of them personally. My reality is that getting a "perfect" (meaning: good enough) take isn't always easy, and I shamelessly lean on every trick in the digital book to bump the quality up a notch and smooth over the imperfections.
But here's the limiting factor. If a performance could be rated on a scale of 1 to 10, all your best editing and processing tricks can only bring it up by 2 or 3 points. And that's if you're pretty good at things like comping and compression and pitch correction and editing. That means a "3" performance isn't going to get higher than a "6".
Consequently, the closer you can get to "perfect" BEFORE engaging any remedial fixes, the better the end result will be. Always.
That comes down to time-consuming rehearsals. You play or sing the part over and over until you can perform it without thinking about it. Not only will you require less post-tracking manipulation, something magical happens once you reach that point: the performance becomes nuanced. You stop reading the lyrics as you sing and start thinking about what they mean, about your timing, breathing, emphasis and enunciation. You no longer have to consciously tell your fingers where to go because they've been there before. You can divert your brain from macro to micro, to the subtle inflections that raise a performance from the mundane.
I would also emphasize that complete perfection is rarely the true goal. Quite the contrary, imperfections are absolutely necessary. That's why I never quantize
anything, never let Melodyne decide what vocal corrections are needed, never worry about breath and fret noises, and almost never comp parts. When I first discovered the miracle of pitch correction, I went overboard with it and horribly mangled a few vocal tracks before figuring out that pitch
variation, not perfection, is absolutely essential to pleasing vocals.