Competitive Edge: It's important to define your competitors too. One should know, what strategies are being used by the competitors to reach to the potential customers. If you know what your competitors are doing, you will be able to modify the plan and maybe your marketing analyst will come with something more innovative that can capture the mass attention.
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.