Developer Dashboard is one of the hidden features in SharePoint 2010. It is turned off by default.

Enabling this feature will help you get critical information such as Execution time, log ID, critical events, database queries, service calls, SPRequest allocation and webpart events.

Developer Dashboard Modes:

‘On’ Mode:
STSADM:

 

on Powershell:

When in this mode, it stays on be default:

 

‘On Demand’ Mode:
STSADM:

Powershell:

You will have to click the icon for the developer dashboard to show:

Disable Developer Dashboard:
STSADM:

Powershell:

Dashboard not shown or enabled.