Here should vocabularies that represent a set of conent objects be placed. Vocabularies that are used only for providing a UI are better placed in the browser code.
Note that you probably shouldn't be importing stuff from these modules, as it is better to have your Schemas fields look up the vocabularies by name. Some of these vocabularies will only work if looked up by name, as they require context to calculare the available options. It also avoids circular import issues.
eg.
The binding of name -> class is done in the configure.zcml