Now in the Form Settings you have two additional options in Submission Settings to limit the number of submissions for the given form:

Limit submissions to one per user:

Allows you to limit to only one submission per user in the form.  If enabled and a user creates a new document when they are the creator on another submission in the dataset the below validation error will display and the submit button will be inactive.

Limit total submissions for this dataset:

Once you click this option you can then 'Enter submission limit' to specify the limit of total submissions allowed in the form overall.  Could be used for a variety of scenarios - for example, a contest app that will only take the first 25 entries. If enabled and a user creates a document when the submission limit has already been met the following validation error will display and the submit button will be inactive.