You can add data without immediately synchronizing.
There might be times when you add some new data in Excel but are not ready to synchronize when you save the list. For example, you might be working with a laptop that is not connected to your office and the SharePoint site.
Just save and close the file without synchronizing. When you're back in the office and you reopen the Excel workbook containing that list, you'll get a dialog box telling you that the workbook has a list that has not yet been synchronized on the SharePoint site. The dialog box gives you the option to click either Yes or No.
Click Yes to keep your changes, and then click Synchronize List 
to update the SharePoint site with the changes.
Click No if you do not want to keep your previous changes, and then click Discard Changes and Refresh 
on the List toolbar. This choice will overwrite the data in your Excel list with the data on the SharePoint site.
Tip You can also use Discard Changes and Refresh to restore your Excel list to the latest published version on the SharePoint site if you want to discard the changes that you've recently made to the Excel list.
