OctoPrint will show you a little icon in the navbar if you have the plugintimings.log enabled:
While the plugintimings.log can helpful while debugging plugin performance, it does come at the cost of reduced performance due to a lot of data having to be written to disk. Thus, OctoPrint will make you aware if you have it enabled so that you can disable it again if this should be unintentional.
You can enable and disable plugintimings.log via Settings > Server > Debug Options.