Does not output flow reports result in longer runtime?

[bonsai]

I am investigating the output of flow reports.

I was checking the flow runtime when the flow report was output at FULL and when it was OFF.

Strangely, the runtime was longer when the flow report was OFF than when it was FULL.
I tested it several times, and it was about one second longer with the OFF setting.

Is this a coincidence?

Or is the report always created, and when it is OFF, there is a movement to delete the report?

[PratikC77703055]

When the report level is OFF, ServiceNow may still generate some execution context or minimal logs internally for system integrity or debugging. These may be immediately cleaned up, and that deletion process can add a slight overhead.

[Mark Manders]

I think everything is recorded and then deleted and not only recorded when it's 'on'. Flows need the inputs and outputs for later reference and I think everything is kept to end in either making it visible or not after the flow is done.

It will help in less log lines, shorter loading times of execution records and such, but while the flow runs, it is collecting the data. 
This has always been my guess (never tested it though). You could reach out to NowSupport to find out for real.