At Looker we sometimes make the tough decision to replace existing functionality with new functionality that we truly believe will result in a better product for all users. When that happens, the old feature becomes a "Legacy" Feature, which allows it to continue functioning for all customers who were already using it, but removes that feature from the product for all new users.
Customers should ultimately transition off of Legacy Features to take advantage of the newer functionality, which is usually simpler, more reliable, or more useful. Once that transition is complete, those customers can then "turn off" the Legacy Feature for themselves in the Legacy Features section of the Admin panel (/admin/legacy).
To ensure that customers don't fall too far behind the engine of Looker progress, we will begin to end of life current Legacy Features. Through this process, we hope to both improve the product and make transitions to new features and behaviors as smooth as possible.
Please note, these changes may require customers to devote their internal resources to migrate off of Legacy Features. This schedule provides a timeline of when current Legacy Features will be formally removed.