The submit()
function is there to make life easier. You can use it on any element inside of form tags to submit that form.
You can also search for the submit button and use click()
.
So the only difference is click()
has to be done on the submit button and submit()
can be done on any form element.
It's up to you.
http://docs.seleniumhq.org/docs/03_webdriver.jsp#user-input-filling-in-forms