Of course there is. On a simple level, consider a parent trying to locate their missing child. Someone might break into their social media accounts to see if there are messages that might help determine their whereabouts.
Consider a website hosting inappropriate pictures of children. Breaking into the server hosting the files and removing them is 100% ethical.
I'm sure you can think of more examples.
Yes it’s true the window net use command is a quick way to discover any shared resources on a computer or server
Cleaning up a system helps clear up the space on the drives. It may also clear up processor usage, ram usage if you uninstall programs that automatically started when the system booted. You may also delete some unwanted programs in the process.
I would say it is considered as science and a bit of maths as its the 'study of abstract machines and automata'
