About saving flow data
There are two benefits from turning on the option to save all data that passes through your flows.
Step by step checks
You'll be able to check on a flow after it has run and see the values for all input and output fields at every step. To do this, click on the Flow History tab. You'll see a list of past executions (if any) in the right pane of the page, and you can click on any execution to see the data from that execution. This is the best way to confirm that a flow is running properly or to determine where an error is occurring. The data is available for 30 days.
If a flow halts before completing due to a temporary failure to connect to a cloud service (even after automatic retries), you'll be able to go back later when the service is available and resume the flow without losing the original data that kicked off the flow.
Click Replay in the Flow History pane alongside the error. You can also replay individual cards one at a time in the Flow History pane by clicking the Replay this card icon on the bottom of the card while viewing a past execution. By default, the card will run using the same values it ran previously, but you can change individual values if you want to correct a one-time problem.