Generally, data retention is a trade-off between the costs of recovering data versus the costs of maintaining the data. Put another way, the less you spend maintaining the data, the more you'll spend to recover it. For instance, tape backups are easy to maintain; however, data retrieval from tape is very labor intensive (expensive). Real-time email archiving on the other hand is automated, and the information can be retrieved very easily; however, there are costs associated with these archiving solutions (although minimal).
The two primary reasons for investing in any information retention solution (besides the fact that it is law in some industries) are quicker disaster recovery and smoother discovery in the event of an audit or litigation. Both are solid reasons to devote some time to this important subject. To get you started, here are the first three things you should do:
1. Understand which regulations affect your organization and what each regulations requires.
2. Publish a data retention policy to all employees so they understand what is required and why.
3. Implement the appropriate information management solution(s) to meet your organizations retention needs and budget.