What does Downgrade Protection track, and why is it especially needed for Customizing objects?

It tracks objects across 2+ transport requests (same or parallel dev systems) and judges whether promoting to a successor system would conflict — a preventive, proactive way to protect downstream systems.

Why critical: workbench objects are locked by TMS until release, but that doesn't apply to Customizing objects → when production systems are shared, the same object changed by different teams = downgrade risk.