It is not only project admins or restrictive admins. None other than the system admins should be able to over ride the global settings at the plan level. It would also be better if there is a provision to disable this over ride at plan level by users (graying out that option) at the plan level by making some configuration change in the bamboo install.
We also probably need a bulk action where we can set the cleaning of the workplace immediately after the build as it is just the user option now and many users do not exercise this leading to lot of space issues.
version 6.8.1 has not resolved this issue.