Evaluating and Reviewing the Plan: Decide a time_frame for your marketing plan and determine the metrics on which you will measure its success. Measure the results it produces and compare them with the expected success. This will help to know whether any corrections or modifications are required to make the plan more successful.
Imagine if you can do all these and manage all these in a marketing plan? Systematic, organized, well thought, innovative and captured all your pertinent business information, don't you find having a marketing plan is useful for your business?