Explanation/Reference:
Explanation:
* You can manage how Microsoft SharePoint Designer is used at two levels:
/ Web application level which is applicable to all site collections in the web application and to the site collection administrators.
/ Site collection level (managed by site collection administrators) which is applicable to all sites in the collection along with the Designers and Owners group.
*Enable SharePoint Designer
Enable ordisable SharePoint Designer 2010 use for an entire application or site collection. If you want to ensure that all designers and owners within a specific site collection can use SharePoint Designer 2010, enable this setting at the site collection level.
Here are the options for managing SharePoint Designer at the Web Application Level:

Reference:https://redmondmag.com/articles/2015/03/19/sharepoint-designer-tool.aspx