I just posted a blog to the Security, Compliance and Privacy blog all about Office 365 Retention, Disposal and Archiving. It's about the differences between Unified Retention, Retention Labels and MRM retention, configurable parameters and other common scenarios.
Take a look if that kind of thing interests you - https://techcommunity.microsoft.com/t5/Security-Privacy-and-Compliance/Office-365-Retention-Disposal...
