Hello! Could someone please break down the potential assumption that could arise from a argument with a cost-benefit analysis reasoning structure?

Would it be that if the author presents X and Y in the premises, then a certain con of let's say, Y, in the premises and proceeds to a prescriptive conclusion of 'one should do X instead' -- the assumption there is that there could be benefits of X that don't outweigh the costs of Y? And so the author just assumed the cost/benefit of a certain option X over Y?

Or is it - let's say we're comparing the cost/benefit of washing hands with hand sanitizer vs soap. The author states in their premises that on the basis of price, washing hands with soap is cheaper than hand sanitizer. Then proceeds to conclude that then, washing hands with soap is the more effective option. Would the assumption there be that the author didn't consider all the costs/benefits of using soap vs hand sanitizer and cannot just conclude which one is better on the basis of price?

Or am I just complicating this and creating new assumptions in my examples lol