Recently seen a citrix forum piece regards this.
User had run an internal security check on the xenapp 7.x environments. Turns out the above policy was enabled on their 7.6 FP2 delivery controller but the user didn’t want it enabled in their 7.1 site so had it explicitly disabled at the policy level. However using certain revisions of the receiver showed up the issue that local drives were still available to user’s launching a published desktop in the environment.
Fix was either one of upgrading the 7.1 DC to 7.6 FP2 or setting local policies to explicitly prohibit access to the local drives.