Plug your gear inventory and weights on GearGrams.com
its a free cool tool, you can generate reports and categorize WORN, CONSUMABLES.
to give you an idea, of starting weight with food, end of trip with less food/water.
Knowing pack weight versus total weight is mildly useful. Example: you get a UL pack, you read reviews that it starts to rip at 30 lbs.
Worn clothes are not in the pack, so you can calculate the gear weight to stuff in the pack before causing it to tear.
I'll play devil's advocate, for the sake of argument.
Worn clothes in excess may cause excessive sweating, over heating. However excess clothes in your pack may annoy the pressure points on your back and waist belt. Also excess weight in your pack may affect your posture.
but a couple of pounds of extra clothes in your pack are not going to turn you into the hunchback of Notre Dame.
Overall, the excess weight of packed vs worn clothes would be negligible.
I understand from my friends that travel airlines, and their luggage are weighed and charged $ per excess ounces at the airport. These guys wear their heaviest clothes, boots, purses on their person, to minimize excess luggage weight charges.
I think this is where the mythology of worn vs packed originated from.