Why does Sales has to coordinate with Purchasing and Production Planners?

There is direct relationship between this three departments . First sales department should expect the sales volume for the next period then the production department demands the row material from the purchasing department to start producing and achieve the organization goals .

All colleagues have given good answers. I agree with them.

Thank you for the invitation 

Work begins marketing research 

And embody is the pulse of the market to know the quality and price and the level of competition 

Then the Purchasing Department procurement process according to the information marketing 

Then start the production phase 

They are connected to the circuit and not separate

The nature of the relationships that must be linked to the marketing department of the most important departments in the organization: 

1-production management: 

If the management function of production is the production of what is needed and requested by the consumer, the task of determining what asks the consumer rests with the management of the institution, which must be informed in a timely management of production, even programmed or modify production processes consistent and desires of the consumer in the product, and then the need for a permanent correlation between the two departments, and vary and means of linkage between one institution to another, in small enterprises are directly the relationship between them, while arise in the organization of large private offices mission is the link between the various departments of the institution. 

2-procurement management: 

Often prefer this administration in large enterprise productivity and be close correlation between them, they are responsible for buying all production requirements, but for the business enterprise procurement management occupies a place of production management in the enterprise productivity, so it will be a close correlation between the two.

Because the budgeting didn't start unless the sales department forecast the amount of unite will sale 

Then production department build there budget based on the sales

and Purchasing department budget the unite needed to purchase during the year to inter production cycle 

AGREE WITH MR MOATAZ  ALI ANSWER 

If it is a production company,

Production department should produce the products that Sales can sell. In this case, Sales should inform Production how much should they produce. Further, Production will coordinate with Procurement to purchase the necessary supplies needed to produce the necessary products. Sales has nothing to do with Procurement department. 

If the company is a reseller,

Sales has to coordinate with Procurement to purchase the products Sales can sell. (Here there is no Production)