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.
Ideas _ people said the more you talk about your ideas the more refine it becomes. I think this is true. Did you ever experience when you talk to more people you generated a lot more ideas? When people give you feedback it triggers another dimension of your ideas? If you are, so where do you keep all these ideas? It should be in a marketing plan.