Khushbu Ghandi puts a padlock on it:
Resource locks are just locks that we can associate to different scopes in Azure allowing us to override permissions at that resource scope and down. When we talk about the scope of the resource lock, we can lock subscriptions, we can lock resource groups and individual resources, and the lock restrictions that we have based off the type of lock we select will apply to all users and roles that have access to that resource. Also, it’s worth noting that locks are inherited by child resources. So, if we apply a lock on a subscription, it is inherited by all the resource groups that have been created under that subscription along with the resources that will be created under the resource groups.
Resource locks come with their own considerations, and Khushbu dives into those. This is a concept I like more in theory than in practice, save for pretty stable systems where you keep things running 24/7.