What are your thoughts on O365 retention policies?  Do you leave it up to users to purge their own data according to corporate policies or have you implemented a system defined policy that purges data automatically?

Moving toward system enforced policies across M365 products.  Some services already have them in place, while others are in the implementation pipeline.

Depends on your business or industry.  Most regulated businesses, like health care, must apply system wide retention due to regulation. You should consult or check the regulations that apply to your business and then decide what is best.  "Trust is good, but the control is better"

Implementing system-defined retention policies in O365 is generally more effective than leaving data management solely to users. Automated policies help ensure compliance with corporate regulations, reduce the risk of data sprawl, and maintain consistent data hygiene across the organization. This approach minimizes the potential for human error and ensures that all users adhere to established guidelines for data retention and deletion, ultimately fostering a more secure and manageable data environment. However, it's also important to provide training and guidelines to users regarding these policies so they understand the rationale behind them.