Save every Step
Enable this feature from Form > Content > Steps Settings.
On every Step change, clicking on the Previous/Next buttons, all partial inserted data will be stored in DB and available for consultation by admins in backend area as not approved Comment.
This extension can track the data entered by the user without his consent.
Check your privacy conditions to protect your visitors.
Every time User change step clicking on Next or Previous, all data inserted will be saved as Comment, and all data will be available also if the User will not end to fill up the form and Submit.