When you try to allocate more resources than your project plan allows, you will get an error that you have exceeded the plan limit.
e.g. If you have a Large plan and if you try to add an app or give it more resource (cpu, memory or disk) exceeding that Large plan then you will see this error:
Error: Resources exceeding plan limit; disk: 8192.00MB > 5120.00MB; try removing a service, or add more storage to your planIn such cases, you have the you can either change the configuration to fit into available plan resources, or increase your plan size.