If you install a third party development tool that is an extension of the Visual Basic Integrated Development Environment and uses Microsoft Repository, the Repository Add-in for Visual Basic will be activated when you install the third party tool. If you are not using such a tool, it is not recommended that you activate the Repository Add-in for Visual Basic. Doing so will introduce overhead that provides no benefit to you.
The repository engine is capable of running without the Repository Add-in for Visual Basic. The Repository Add-in is only required to keep the MDO Model instance data synchronized with your Visual Basic projects. Consequently, if you install a third party development tool that uses Microsoft Repository, but does not use the MDO Model, then the Repository Add-in for Visual Basic is not required and will not be activated.