This is really just a “note to self” because I always forget where this settings lies.
Activate On Default is property of a feature. You can find it by opening the Feature Designer and then looking in the properties window. It is the first property under the SharePoint section.
This property determines whether the feature will be activated when the solution is activated. My preferred approach when developing a publishing portal that requires web templates, is to only have the ‘web templates’ feature activated this way and have any/all other features activated along with the root site web template.
Note that this property has no impact on the set of features which are activated when deploying the solution via Visual Studio. You can configure this somewhat using the ‘Active Deployment Configuration’ property of the project. You can try something like the following from Mavention for more granularity: Mavention – activating selected features