So, at last, we arrive at the big question: what needs to be stored in our database? You might be tempted to go with the simple answer: everything. A lot depends on how many unique individual data items we deal with and how many of each can we expect. Your initial tendency might be to take the easy route and just store everything: storage is cheap, and a MongoDB installation can be scaled up easily through the process of sharding.
It is in your interest to economize, however, if for no other reason than to avoid having the database engine clogged up with massive amounts of unneeded data. Also, no matter how cheap it is, there will be only so many times management will grant your request for a purchase order to buy more storage! Furthermore, the less data your application needs to sort through, the more efficient it will be.
So, to answer the question, you should store any data items...
