The Apps allowed to run and Apps blocked from running policies control which apps are allowed to run on a device.
If an app is prevent from running on a device by either of these policies, it will be hidden from the home screen and cannot be launched by any means. Blocked apps are not uninstalled from the device, merely hidden.
If you configure Apps blocked from running, any app listed in the policy will be hidden and blocked from running. Any unlisted app is not affected.
If you configure Apps allowed to run, this policy acts as a whitelist and any app not listed in the policy is hidden and blocked from running.
Overlapping Policies
If both Apps allowed to run and Apps blocked from running are configured on the same device, the policies will be merged and the net result is that apps listed in Apps blocked from running will be removed from Apps allowed to run before the policies are delivered to the device.
For example, if Apps allowed to run lists Apps A, B, C while Apps blocked from running lists B, the end result is that A and C will be allowed to run on the device.
However, if your Apps allowed to run policy is configured with a higher priority level than your Apps blocked from running policy, no changes will be made to the allowed apps list. Blocked apps policies can only override allowed apps policies at an equal or lower priority level.