Have you ever had someone filling out a form and they're in such a rush that they don't type their e-mail in the proper format or even forget to finish typing it in?
​
You can turn on Field Validation for any field and choose Email Address and it will not let the user submit the form unless they have typed in a valid email format like name@domain.com

To do this you will hover your mouse over a text field and then click on More Options.

Then once you are in the Advanced field options menu you will scroll until you get to Field Validation and choose E-mail Address:
​

This is not only helpful with ensuring that the proper email address format is received but this is also required for certain features like Submission Receipts and Triggers.