Why is sales planning necessary?

There was AA time before when customers had more time and sales was a simpler job. As time passed, sales job became much more complex and the pressure on the salesperson to make good decisions about the effective use of his time has never been greater. Salespeople nowadays have much pressure and need to confront a number of things and requires a lot of decision making as to which customer to invest their time in and choose their activities to do. It is important they need advanced planning.

For a complete strategic planning, please refer the link in sources. Hope this helps.