What these two switches decide
The Zite mobile app works offline. It keeps a copy of your project on the phone, and it holds the forms you complete until they are sent. That means two things need to happen regularly:
Sync brings the project down to the phone: new sites, forms and tasks.
Upload sends your completed forms up to Zite.
Out of the box, you do both yourself from the Sync sheet. Two switches under Account Settings → Sync let the app do them for you instead:
Auto Sync refreshes the project every time you open the app.
Auto Upload sends completed forms with every sync.
The next page shows where the switches live; the two after that explain each switch in turn. How syncing and uploading work day to day is covered in Work offline and sync.