Should suppliers be more involved in project planning?

Suppliers are an essential part of the supply chain, but how involved should they be in project planning?

Some say the more the better to avoid surprises. Others argue that too much involvement only leads to more complexity.

How do you handle this? Do you rely on close cooperation with your suppliers or do you keep your distance?

Share your experiences and strategies to find out how to best integrate suppliers while balancing efficiency and complexity.