This service will automatically start when the system boots up and keep running with your system.
If it consumes RAM/CPU/disk usage abnormally, your system performance will be negatively impacted.
How to Fix Diagnostic Policy Service High CPU Usage?

When the size of the file grows extremely large, Diagnostic Policy Service high CPU usage will appear.
In this condition, it’s possible for you to delete the file inTask Manager:
Step 1.
Right-choose thetaskbarto selectTask Managerin the context menu.

Step 2.In Processes, scroll down to findService Host: Diagnostic Policy Serviceand right-tap on it to chooseEnd Task.
In the confirmation message, tickAbandon unsaved data and shut downand pressShut down.
PressWin + Rto open theRunbox.

FindDiagnostic Policy Serviceand right-select it to chooseProperties.
InGeneral, hitStopandOKto stop DPS.
Open theRunbox again, jot down%WinDir%\System\sruand hitEnter.
Typeedit power planin thesearch barand hitEnter.
PressChange advanced power controls.
In the new window, expandWireless Adapter SettingsandPower Saving Mode.
Set bothOn batteryandPlugged intoMaximum Performance.
PressOKto save the changes.
Clearing the logs can help to handle Diagnostic Policy Service high CPU usage.
TypeRunin thesearch barand hitEnterto open theRunbox.
Typeeventvwr.mscand hitEnterto openEvent Viewer.
In the left pane, pressSave All EventsAsto save the current event log.
As soon as they are saved, hitClear Log>Clearto delete them.
Repeat all the steps above forSecurity,SetupandSystemunderWindows Logs.
At last, dont forget to reboot your setup.