You did know, didn't you, that one record in Salesforce takes up 2kb of your data storage - even if it only has data in one field, or data in hundreds of fields. This doesn't seem too bad until you start getting data that grows exponentially and you wonder where your data storage is being eaten up. Data from Salesforce is !#$ing expensive. Before you rush out and give Salesforce more money, think about how you may be able to reduce data storage. 

A great comment "just like a house it's probably smarter (definitely less expensive) to clean out your closets each spring instead of keep on building new rooms onto the house"

Things that can cause data storage to grow:

Things you can do to reduce data storage:

Technical notes on data storage: