Is compliance something that is important to you?  If so, many people may not realise that standard field history tracking in Salesforce is kept only for 18 months.   This is clearly insufficient in most regulated industry scenarios.  It is possible to use Apex in this scenario to write changes into a separate object however if you need to audit changes across your system for 7 years then you might need to consider the 'Field Audit Trail' add-on.