Sales and Strategy Forecast: If you have a target to achieve you can plan out your work according. It's just like keep the figures real and amenable. Unrealistic figures would not help you ever to get the target on time. Secondly with these forecast, you can compare your marketing strategies and come up with the best solutions for future activities.
Therefore, a marketing plan, according to Kotler, is a "written document, which includes the objectives, strategies and action plans regarding the elements of the marketing mix which facilitate and enable compliance with the strategy dictated at the corporate level".