To increase the performance of the site, can we disable the SharePoint 2010 developer dash board using powershell ??
Developer dashboard should be enabled only when you see some unexpected behavior (delay in loading webpart etc) and want to see what part of page is taking more time.
Enabling it will surely affect performance of your SharePoint site since it will have to load the calculations.
It is always better to keep it off when everything is well :)
If needed, You can enable developer dashboard on demand only.
See Section 5. Developer Dashboard here for details: