That is entirely up to you but it is what I would do. The moduleguid can be useful for implementing a content delete handler to delete related rows from your table when the module instance is deleted.

moduleguid and itemguid can also be useful if you want to use our built in content versioning to keep a history of changes in edits to your feature and could also be useful for example if you wanted to use our built in comment system to support comments on your feature items or if you wanted to use our content rating system etc. In other words moduleguid and itemguid cna give you somethign to store in those related tables if you choose to use them and it gives you a way to retrieve the related rows from those tables.

You can study built in features to learn about how to implement content delete handlers or how to leverage other subsystems such as content rating, comments, content history etc.

Hope that helps,

Joe