Diki, I think what's being referred to is two things.

1. Gain staging to optimize the total output/volume of the system.

I remember my first few times with the Bose. I would run out of steam i.e. not be able to go very loud and very little headroom (I thought great, this damn system IS just an underpowered computer speaker system!!)

Then I Trimmed each channel correctly and could run things just as loud as I needed.

2. T1 Settings.

The mixing desk can be a tricky little beast at first - LOTS of options (which really means just more control over things, fortunately) and lots of presets. e.g. every channel has an optimized EQ setting for commonly used industry standard mikes and equipment.

For example:
I could set up Channel 1 for an SM-58, Channel 2 for MP3 playback (and several settings within THAT just for different types of music playback - soft/loud etc) Channel 3 Could be for Guitar FX/Amp Modeling (it even has specifics for things like a Line 6 Pod) Channel 4 could be for Keyboards.

So that's the output and tone optimization you can and should go through.

Hope that helps explain things.