You're absolutely right. For what it's worth, it's just the first part that's important.

When you pick up a new concept from a "resource" such as a tutorial, take a minute to explore the concept and understand the semantics of what you're doing. In the name of illustrating a concept tutorials can often be misleading in subtle ways.

An explanation of my "useless use of cat" example:

The command line has a concept called "piping". This lets one command send output to a second command. It's very handy. There is usually also a "cat" command, which will read a file and send the contents where you tell it. This is often your screen, or through a "pipe" to a second command. There is also a "grep" command that lets you search data for certain words.

Many "linux newbie" tutorials combine these tools to show how "piping" lets you send data from one command to another. "cat" some text file, then "pipe" the output to "grep" to search for your words. It usually looks something like cat ./my_address_book.txt | grep Giles to find lines in "./my_address_book.txt" that contain the word "Giles". The thing is that "grep" can take a file name as an argument. You can just do grep Giles ./my_address_book.txt, and cat is for concatenating files into one. If you want to simply read a file there are more appropriate tools such as "less". This by the way is the "useless use of cat"

When you're a newbie though, it may be the first time you're seeing either "grep" or "cat". The tutorial is just trying to show you "pipes". Along the way you're picking up these "bad habits". I've met professional sysadmins who didn't know grep took a filename as an argument. It was always "cat blah | grep my_search". I will see people type "cat /some/file | less" instead of "less /some/file". It shows a lack of understanding of what these tools actually do, and IMO it just comes down to regurgitating tutorial actions without bothering to understand the semantics of what you're being shown.