Hi - Usually the sounds out of something like the trinity are already very processed, and adding compression just for the sake of adding it will do more harm than good. Now, there may be a case where a trinity patch isn't sitting right in the mix, and compression might fix it, but as octoruss said, this is a case of using it as a tool to correct a problem. The only thing I *almost* automatically reach for compression for is vocals. They usually need it, though sometimes a track calls for a raw vocal. As a general rule, the time to add compression is when the track is lost in the mix, but when you bring it up it sticks out wrong, and you just can't get it in between.
Having said all that, I also refore to rule no...... 1 experiment, experiment, experiment.
Cheers, RD