Landscape tries to request as little access as possible for users of the free, open-source version. No write access to code is required. The following GitHub permissions are requested:
For users with private repositories, complete read and write access is requested. GitHub does not have nuanced permissions for private repositories.
One problem is that you can only give Landscape access to all private repositories. If you belong to multiple organisations, this can be difficult as perhaps not all will want to allow that.
In this case, you can ask the administrator of the organisations to enable approved applications - this means that the organisation administrator can create a whitelist of which applications are allowed to see their private repositories. It is not enabled by default.