When you start a shell session, it opens in your home directory. This is true in all OSs, and even the paths are similar.
In Windows:
C:\Users\username\
In Mac:
/Users/username/
In Linux:
/home/username/
or
/users/username/
Why home?
It keeps your stuff segregated from other peoples’ stuff: see the Documents, Downloads etc. directories.
It is highly protected against other users, because of both its own permissions and because of the permissions of the directory above it. That’s what makes /home an ideal place to create a subdirectory and share it.
It gives you a separate programming (scripting) space for your own work. create a bin/ folder in your home and add it to your PATH variable for an easy way to test your scripts.
It lets you set your own preferences for everything you use: web browsers, text editors, terminals/shells, etc. Note all the files and folders with names that begin with a dot. That dot marks them as hidden files.
It gives you a place to share your web pages. Usually an ISP, for instance, will give you an html/ or www/ or similar-name directory for your personal site.