title: mongodb/mongoose - when to use subdocument and when to use new collection
body: <p>I would like to know if there is a rule of thumb about when to use a new document and when to use a sub document. In sql database I used to break all realtions to seperate tables by the rule of normalization and connect them with keys , but I can't find a good approch about what to do in mongodb ( I don't know how other no-sql databases are handled).
  Any help will be appreicated.
  Kind regards.</p>