Recently we were working on developing custom share point workflow which basically operates on any share point list/document library. We created a feature to activate/deactivate this workflow on sites.
Initially I had given the scope of this feature as "Site" (i.e. a site collection feature), later during code review I felt that as this feature and workflow basically operates on list and does not have any kind of dependency on any other list or item on the site collection I thought making the scope of this feature as "Web" (i.e. a Site Feature) is fair enough. When I restricted the scope of this workflow feature as "Web" and tried activating I got the error as "Elements of type 'Workflow' are not supported at the 'Web' scope. This feature could not be installed".
Through this I came to know that whenever we create a feature to activate/deactivate workflow the scope it should be Site (i.e. The workflow related feature should always be a Site Collection Feature).
