The RetailCdxSeedData class runs whenever this option is triggered in Dynamics 365 for Operations:
Retail and commerce → Headquarters setup → Retail scheduler → Initialize retail scheduler
If you've added custom tables that need to sync between HQ and the Channel Database via CDX (Commerce Data eXchange), extend RetailCdxSeedData to include them.
Skip that step, and you're stuck doing the CDX table mapping by hand — in every environment, and again after every database refresh. That's not just tedious; with enough tables, it's easy to miss a field.
For how to customize the class with an extension, see CDX extensibility on docs.microsoft.com.