The ENV variables set in ConfigMaps then refered in Deployment. In this case need to do first create ConfigMaps then should create a Deployment.
If don't follow this order, created a Deployment first the Pods will be fail will say that ConfigMaps not found.
While running Kubectl command we need to follow the order but in Helm will take care of that order.

The only Deployment like Pods will be rollback to the previous version by using Kubectl.
Helm Chart can completely rollback to the application state such as Deployment like Pods, Services, ...etc.