To disable the declarative workflows go to Central Administration site and select the Web Application. under General Setting there is a menu item for controlling the workflow for the Web Application:
If we try to create a new workflow using SPD following error will be displayed stating "User-Defined Workflows have been disabled by the SharePoint Administrator. User Defined workflows will be unable to run."
Also once these workflows are disabled many predefined workflows are not available to be used in the site collections. Only Disposition and Three State Workflows are available to be used.