The trim pot doesn't change the tone from the instrument, it only changes the amount of signal sent from the instrument to your amp. For some amps, too much signal from the instrument may overdrive the amp's preamp stage.
As Kevin stated, you can use your trim pot to adjust the output of your Orion to match the output of some other bass you play on the same show. Thus you can set your amp up to expect the same amount of signal from both basses.
Like the Essence, Persuader, Epic, and Excel, the Orion has one preamp, and thus one trim pot. The other models have two preamps, one for each pickup, and thus two trim pots. With two trim pots the outputs of each pickup can be adjusted relative to one another.
I tend to think that in order to minimize the amplification of noise in your signal chain, it's a good idea to send as much signal as possible from the instrument to your amp, as long as your amp can handle it. I'm thinking that it makes more efficient use of your amp's power. But I would imagine that the relationship between instrument output and preamp tube saturation is probably a bit more complex than that. So you may want to experiment with adjusting your trim pot and seeing how that effects your amp. You may find a sweet spot that works well for your rig.
