I have to admit I saw this post yesterday and have been thinking over why it would improve campaign execution times... do you have selection criteria that uses history? If so, having a partition on CONTACT_DT and always using a date range could be of considerable benefit.
As far as best practices go, this is more of an organization-by-organization decision based on campaign requirements (selection criteria use cases, as I mentioned above) and reporting and/or analytical requirements. Moving old records off to a data warehouse would allow you to develop historical reports (different from what I would consider your operational campaign reports that are run against the CDM). Creating some DI Studio jobs (or other ETL) to schedule this kind of housekeeping is probably your next task.