Dynamically set form fields with url parameters. I would like to specify that this is commonly used for Hidden form fields.
Hidden (or not hidden) field ID: utm_campaign
Upon loading the page the hidden field will be populated with: "big event"
Once submitted, you will know what URL the user came from.
Why this is important:
This allows marketers to track where leads/ purchases come from and attribute them to events (big event), emails, ads, social posts, etc.
Instapage (Built for marketers) relies on this feature, take a look here: https://help.instapage.com/hc/en-us/articles/115005969527-Passing-UTM-Parameters-From-The-URL-To-A-Hidden-Field