sucommand is for switching to another user. This is useful if you need to run a lot of commands or manage a lot of files as that user.
suis a bit dated and most operations should be done via
sucan still be used form time to time.
sudocommand can also be used to switch to a user, but it's primarily function is to switch to the user, complete a task, and then "exit" that user session.
The benefits of
sudois the ability to control what the user can do on a granular level. The
sujust an all-in command: you simply become the user and can do anything that user can do. With
sudo, you can control that down to specific commands.