What this is
Commercial marketing rather than campaign marketing. Where the spend goes, what it returns, and how to keep making that judgement when attribution is imperfect, which it always is.
What usually brings people here
Rising costs, flat return, and a channel mix that grew by addition rather than decision.
What I do
I look at contribution rather than last click, find the channels doing work nobody is crediting, and cut the ones surviving on reporting quirks.