So now we have 'Standard Trims' as well as standard loadings?
Agreed a 'normal' loading based on pre-disposed conditions (full load upstairs)can result in a quicker turn-around for some aircraft types.
However, if you are loading both ends anyway then you still have the same amount of bags going up two belts hence a non-standard loading will take just as long or short a time.
If your loading only one end it doesn't matter.
Restricting passenger seating (and/or up/down grading on schedules)should be a last resort under any circumstances (if it is used any earlier I see that as not doing one's best
- sorry) and a deviation from a pre-ordained loading instruction a better option.