A system's criticality classification is important in large organizations because it provides for proper prioritization and scheduling of security and maintenance tasks. A system's criticality classification is the level of importance or impact that a system has on the organization's mission, objectives, operations, or functions.
A system's criticality classification may depend on factors such as the system's availability, integrity, confidentiality, functionality, performance, or reliability. A system's criticality classification helps the organization to allocate resources, implement controls, perform audits, apply patches, conduct backups, and respond to incidents according to the system's priority and risk. A system's criticality classification does not necessarily reduce critical system support workload or the time required to apply patches, as these may depend on other factors such as the system's complexity, configuration, or vulnerability. A system's criticality classification may allow for clear systems status communications to executive management, but this is not the primary reason for its importance. A system's criticality classification may provide for easier determination of ownership, but this is not the main benefit of its importance.

Segregating environments ensures that code changes are developed and tested in isolated, lower-risk environments before being promoted to production, reducing the risk that untested or insecure changes disrupt live operations, and helping limit unnecessary exposure of sensitive production data to development and testing activities.

Reference:
RESCORLA, Eric, SSL and TLS: Designing and Building Secure Systems, 2000, Addison
Wesley Professional; SMITH, Richard E., Internet Cryptography, 1997, Addison-Wesley
Pub Co.

The best method used by a forensic examiner to isolate the powered-on device from the network and preserve the evidence is to put the device in airplane mode. Airplane mode is a feature that disables the wireless communication functions of the device, such as cellular, Wi-Fi, Bluetooth, or GPS. Putting the device in airplane mode can isolate the device from the network and prevent any remote access, modification, deletion, or wiping of the data on the device. Putting the device in airplane mode can also preserve the evidence by maintaining the current state of the device, such as the battery level, the signal strength, the date and time, or the notifications. Putting the device in airplane mode can also avoid any legal or ethical issues that may arise from intercepting or monitoring the network traffic of the device. Suspend the account with the telecommunication provider, remove the SIM card, and turn the device off are not the best methods used by a forensic examiner to isolate the powered-on device from the network and preserve the evidence, although they may be possible or alternative options. Suspend the account with the telecommunication provider is a method that involves contacting the service provider and requesting them to disable the service or the account associated with the device. Suspend the account with the telecommunication provider can isolate the device from the cellular network, but it may not isolate the device from other wireless networks, such as Wi-Fi or Bluetooth. Suspend the account with the telecommunication provider may also require a court order or a warrant, and it may alert the owner or the user of the device. Remove the SIM card is a method that involves physically removing the subscriber identity module (SIM) card from the device. The SIM card is a small chip that stores the information and the credentials of the user and the service provider, and it enables the device to connect to the cellular network. Remove the SIM card can isolate the device from the cellular network, but it may not isolate the device from other wireless networks, such as Wi-Fi or Bluetooth. Remove the SIM card may also alter or damage the data on the SIM card or the device, and it may require special tools or skills.
Turn the device off is a method that involves powering off the device completely. Turn the device off can isolate the device from all wireless networks, such as cellular, Wi-Fi, Bluetooth, or GPS. Turn the device off may also prevent any further data loss or corruption on the device. However, turn the device off may also cause some data to be erased or overwritten, such as the data in the volatile memory (RAM) or the temporary files. Turn the device off may also trigger some security mechanisms, such as encryption, password, or biometric lock, that may prevent or hinder the access to the data on the device.