In addition to what Rich said, if your trim pot is all the way up, it may overdrive some amps and preamps; thus you can back it off to where that doesn't happen. And I believe from what some folks have posted to the group, that the same thing might apply to some stomp boxes. But changing the level does not affect the tone of your bass. As far as an optimal setting, if balancing with other basses and overdriving amps is not an issue, then I'm thinking you may want to set it on high. I could be wrong, but my thinking on this is that by getting as much signal from the bass as possible, you don't need to add as much gain at other stages of the signal path; thus the amount of noise added to the signal should be less.