A participant completing a survey on EngagementHQ has the ability to save a submission only under certain circumstances. These circumstances are;
The participant must be registered and logged in
The survey needs to be designed and published as a multipage survey
For a single-page survey, any data entered will only be saved if the submit button is clicked. Navigating away from a single-page survey will lose all data and the participant will be required to start again.
For multi-page surveys, the responses of the completed pages (not the current page) will be saved locally until the final submission of the survey. This allows participants to complete several pages of a survey and return to the survey at a later stage to complete the activity.
Note: As can be inferred, anonymous participants will always have to start afresh.
Read about creating multi-page surveys in the article on create long surveys with multiple pages and section headers.