Event registration form
If you are hosting an invitation-only event, you can limit the number of requests submitted by those willing to attend.
Homework submission form
Limit the number of applications for online courses and give students the opportunity to submit homework twice.
Voting forms for Сontests
Restrict the number of voting form submissions by the user’s IP address, so that the vote from one IP is counted once.
Job application form
You have a vacant job opportunity and you want to limit the number of job application forms.
Online survey
Send out the survey results with a limit by 1 time to maintain experimental integrity or open the form only a logged-in user.
User registration
To prevent the army of bots from spawning the registration form should be submitted only once.
info: https://jetformbuilder.com/addons/limit-form-responses/