Some data forms part of your Application's structure and should remain consistent between source and target environments. This data can be kept in sync (connected) and deployed through Test & Deploy. Other data is operational and is managed independently (disconnected) in each environment.
The default behaviour depends on the type of model object:
Dimension List Items are connected by default because they typically define your Application's structure.
Metrics are disconnected by default because they typically store operational data. Metrics can be kept in sync when their data forms part of your Application's structure.
The following articles explain when to use connected and disconnected data, the considerations to keep in mind and how to configure each option: