The leaflet is a material designed for short contact; the reader allocates seconds to it, not minutes. So the most important decision of a leaflet is how much 'net' the content is, not how much'. A single main message, a few proofs that support it, and a clear next step that is the skeleton of a good leaflet.
The folding logic is the backbone of design: each floor should prepare the reader for the next information when it is opened. On the cover there is curiosity, an inside explanation, and on the back there is communication and call. When the visual-text balance is disrupted, the leaflet feels either empty or suffocating.
When designing a corporate brochure, my goal is that if someone took it off the table and looked at it for three seconds, they would understand what you're doing and why they should talk to you.