Cost benefit approach
This approach determines whether the input is outweighed by the outcome of marketing. Ideally if you are not going to exceed the efforts that will be put into the plan then it may be worth revising it or scrapping it completely.
There are monetary costs associated with marketing (advertising, staff, and time). This needs to be accounted for when completing your plan. A budget should be prepared detailing all costs involved and what the benefit would be from instituting the plan.