Legacy environments or environments using a lot of IoT devices may still have older protocols such as Telnet or Berkeley r-commands in play where SSH would be a more appropriate solution.
These protocols are transmit over the network in plaintext, unencrypted form, which leaves them vulnerable to TCP session hijacking, sniffing, and other forms of cyberattack.
As such, it is important for incident responders to be aware of these services and how they may be abused as they provide remote read, write, and execute primitives to an attacker.
https://en.wikipedia.org/wiki/Berkeley_r-commands