Aspects are a key piece of getting results with EFT. If you tap an issue down to zero but the issue still remains then in many cases there are other aspects of the issue that need to be resolved.
An issue like fear of flying might be addressed and released by just tapping on "Even though I have this fear of flying....." 5 minutes later and the issue is gone. Great!
But its not always that easy. Typically there is more depth to the issue. Or in other words there are more parts of the issue. We call these parts aspects.