i fly a lot with another ppl and we have often discussed crm training and ppl in ga. Whilst this is not a multi crew environment even in the twin there is always going to some interaction. This may be as you say just in the go no go decisions but in the air there are lots of issues that one will discuss as the flight progresses.
We always discuss how the non flying pilot could help in an emergency and what they could do to help in that event. I have wondered if there was something the ppl flying as p1 in a single pilot craft with another pilot could learn from all the lessons taught for crm in a multi crew setting.
I agree io that often one feels differently about go no go decisions when more than one reasonably experienced ppl are flying together