Process Deferred Rollups Action

By itself, the Process Deferred Rollups action doesn't do anything:

With that being said, it's an important action to add into your flows whenever:

• you're using the base invocable action with the Defer Processing option set to {!$GlobalConstant.True}
• you're using the CMDT-driven action and either you haven't toggled the Defer Processing option (it defaults to true within this action), or you've toggled the Defer Processing option but still have it set to {!$GlobalConstant.True}

If you're unsure about whether or not to add this action or not, you can always add it to your flow after all Rollup actions have been declared; there's no harm in having it!

Why Should You Defer Rollups?

Since it takes memory to defer rollups, the thought process behind wanting to defer them might be counter-intuitive, but apex-rollup works best when all rollups are queued up at the same time. This allows the framework to process rollups in the most efficient manner possible, minimizing the number of parent-record updates that need to be performed and the number of queries that need to be issued. If you have more than one rollup configured using the base invocable action, I would highly recommend deferring each one of them and adding this action onto your Flow's path after configuring them.