As data professionals, we plan for things. We plan for growth, we have a disaster-recovery plan, we have a plan for consolidation. Those are all good things. But I've seen very few shops that have a good data retention plan. This is a plan that basically answers the question, how permanent does that data need to be? Just like the disaster recovery plan, we have to ask the organization what they want, and just like that DR plan they'll tell you they want it all. In the case of the DR plan, they'll say "we don't want any downtime", and when you ask them how long to keep a set of data they will say "forever". But both of those things come at a cost. Not only is there a storage cost, but as the data grows your window for maintenance, backups and optimization grows.
So take some time today and put that retention question on your roadmap. I know, you have a lot to do, but if you don't at least open the discussion now, you'll have a lot more to do in the future.