working on web form with 5 fields, once i fill all the fields, i usually clicks the submit button. Is necessary to give similar action to "Enter" key for submission?
Different people are going to use the form and it's a good practice to serve the need of those different computer users. Power users will rely heavily on the keyboard and will tab through the form and submit it by pressing enter. So for those users: yes it would be nice to implement this.
For novice users who click on most fields and buttons this seems a bit overdone. However, they would benefit from other features. Like disabling the submit button after it is clicked so double-clicking that button would have the same result.