As a fiction writer predominantly, tone and voice are actually the engine for all my writing. It's what I lead with, and what gets me out of problems in stories. When everything in a story has to line up with the tone and voice, it makes it a lot easier to see what doesn't fit and isn't working. An analogy would be if everything that is in line with the tone/voice is purple, and everything that isn't is orange. Revised the orange pieces until it all feels like the same story. That's not the only thing that makes a good story, but I think it plays a big part.