Several of our client clubs have used forms for things like voting on a slate of proposed board members where votes should be limited to one per account. We can accomplish that by using the Limit Form Submissions tool.
Limit Form to Logged In Members
The first step is to make sure the form is only accessible to logged in members. Go to the form in question and then click on Form Settings. Scroll down to the section labeled Restrictions and configure it as follows — changing the message to whatever you would like non-logged in people to see.
There are a number of options for limiting submissions (covered in detail here: https://gravitywiz.com/documentation/gravity-forms-limit-submissions). For this example we're going to limit voting to one vote per account.
Under the Settings for the form choose Limit Submissions.
Click on Add New to set up the rules for the feed. The fields are configured as follows:
Limit Feed Name: Can be anything you wish. It's possible to set up multiple feeds per form based on different conditions (ex: one limit for members, another for non-members) and the name is just for your reference.
Submission Limit: The number of entries that will be allowed based on the feed rules -- 1 in this case.
Time Period: You can set limits per week, month, etc. In this case leave the default value, Forever, to restrict entries to one per account.
Limit Message: This will be displayed in place of the form if a member has already voted.
Rules: You can combine various fields from the form into order to enforce the limits. In this case we only need a single rule with the conditions set to User and Each User.
The full settings would look like this: