The Microprofiler will remain running on the client regardless of whenever or not it is actually On or Off. This of course will cause the Microprofiler to eat up system resources for absolutely no reason hurting framerates on weaker systems. The performance impact is entirely reliant on how much a experience actually utilizes and displays things on it. Larger experiences with more code going on tend to be the most costly on the Microprofiler.
A fix to this would be very helpful and likely increase average framerates across all games.
Workaround:
Enable the Microprofiler through the Settings page.
Click on the “Pause” button from the Microprofiler interface
Hover over the “Mode” drop-down.
Click “Off”.
(You will need to repeat this process every time you restart the client. Also, disabling it in the client settings page after pausing it will only cause the microprofiler to resume)