This is not a Traditional v UL debate!
You've just been invited to hike in a completely new environment.
just a few examples to get started.
1 New trail- not sure about water do you carry xtra or stick with what you would normally carry
2 Fire- carry starter or just stick with trustworthy old bic
3 Clothes- its summer but your going above 6000ft do you take heavy clothing
4 Safety-is a two way street carrying xtra will slow you down and take a physical toll thus increasing the possibility of injury but if the weather turns on you that heavier sleeping bag and or tent can make the difference.
5 You just plain don't know what your doing.
This is open ended so feel free to use any of these or your own.