What is the purpose of the critical flag for Resources in the Simulation Set

In a Constrained Supply plan with ECC, Resources are hard constrained if

case 1:

"Plan option Enforce resource capacity constraints is checked" and "Plan option Critical Item-Suppliers and Resources for Applying Capacity Constraints is checked" and the resources are marked both "Bottleneck" and "Critical"

(or)

case 2:

"Plan option Enforce resource capacity constraints is checked" and "Plan option Critical Item-Suppliers and Resources for Applying Capacity Constraints is unchecked" and the resources are marked "Bottleneck".

Would like to understand in what scenarios the Critical flag will be helpful as it functions the same way as the Bottleneck flag.