Why you need to create and force user to be able to write on a samba share?

I had a problem on my samba share, that even adding writable on my smb.conf, I still couldn’t add any folder/file on it. After searching, I found this answer, but I still don’t understand.

Some people say that you can solve the problem too by changing the permission of the folder to 777, but:

  • Why does this actually works?
  • Why can’t you just let the directory with the root as the owner and with the default permissions?

I found an answer on another post that almost makes me understand, but I still don’t get it