I have seen this debated when two folks decide to do a thru hike. The main reason given for not wanting to share is the consequences if the pair decides to part ways mid way through. Not as much an issue for a weekend trip but I like having the option to alter plans and sharing gear would make that a bit complex. I think that happened on your Rae Lakes trip for example.
Also in my case there would be almost no advantage from a weight perspective. My total shelter weighs 1 lb between the tarp and bivy. My two person TT Squall weighs about two lbs so no advantage there. My stove only weighs maybe 2 oz. and would still take the cup. And then someone has to potentially wait to cook.
And first aid, maybe but even that is so minimal unless you had a large enough group.
Bottom line… 2 oz. savings just isn't worth it.

