Although 85% of database content is inactive this does not mean it is possible to discard it immediately. Inactive means the data is not a part of present-day business activity but it will be needed at some indeterminate time in the future AND it has to be kept for a minimum period of time before it can be discarded. In short, inactive does not mean unnecessary. There is a life cycle for data, a simple definition for the data life cycle might be:
There are many examples of this life cycle. An everyday example is activity in your bank account. As follows:
Active: A withdrawal is noted in a transaction ledger by your bank.
Recent: The withdrawal appears in your statement.
Historical: The bank makes sure the transaction is remembered (legal requirements) for a guaranteed amount of time.
Expired: The details of the withdrawal no longer need to be kept for legal reasons, they can be discarded.
A similar overall life cycle applies to different sorts of data. For example, closing a back account will pass through the same sort of life cycle, the timings may be different but the overall process is the same.