Deez, if I understand your question, then the answer is "kind of".
Assuming your vocals that you tracked really loud (say -3 for the sake of argument) are not distorted, then YES, you should use the trim to bring them down lower (-12 to -18 or thereabouts) pre-fader when you mix. That will correct the gain-staging during mixing issues and you will get a very subtle boost in quality. What it won't do is help the quality of the vocal that was recorded. When you track really hot you run into the non-linearity portion of your A/D converter. This is a bigger issue on cheaper converters than it is on nicer ones, but in generally you try to avoid it when conveniently possible. That non-linearity would very subtly degrade the quality of your vocal and once it's recorded that way you are stuck with it.
We are talking about very small amounts of sound quality here. But if you are trying to compete with huge records out there, every bit helps.
