Pitching your services?
Keep it short.
Attention spans are short. Shorter when someone is trying to sell us something.
Building a policy or strategy?
If you want a strategy to succeed, you sound probably add details.
Engineering a bridge or a nuclear reactor?
You’re going to need extensive drawings and granular details.
Simplicity isn’t about length. It’s looking to create something as short and easy as possible…but not too short and easy.