all of us know the usage and benefits we get using Developer Dashboard in SharePoint 2010. But This Dashboard is not enabled by default in SharePoint. You (The SharePoint Administrator) can enable it using either STSADM or the SharePoint Management Shell.
Here, you will see how to enable Developer Dashboard using PowerShell, and the options you get for the Dashboard mode.
Start by opening SharePoint Management Shell, you can find this by going to Start>>All Programs>>Microsoft SharePoint 2010 Products >> Right click the SharePoint 2010 Management Shell and choose Run as administrator.
You need to know that there are 3 modes for the Dashboard, which are On,Off, and OnDemand.
These modes explain themselves. On Mode enables the Dashboard so the Site Collection Administrator will view it whenever he opens the page, he doesn’t have the option to turn it off. The Off mode Disables the Dashboard on all pages and the Site Collection Administrator has no option to get it on. The OnDemand option makes it possible for the Administrator to turn it on or off when required.