To restrict on which holder you can drop a control you have to use Sitefinity's layouts. Once you drop a control you can choose "Permissions" from "More" option. Please take a look at the attached screenshot(permissionslayouts.png
). On the next window there is a permission option "Drop widgets or layout elements"
You should perform the same steps if you want to make restrictions on widget level. Each widget has a "More" option where you can go to its "Permissions"
And the second option is working with policy. You can set different policy per role or user. The policy works with configurations and this allow you to have different configuration per role or user. When you go to Settings you can delete or create Config elements, but you cannot set permissions on these elements. You can take a look at policysetup.png
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