You can currently 'View all' data in the various sections of the API with GET requests. For example:
domain_URL/contacts.xml
domain_URL/helpdesk/tickets.xml
This will return all the data FreshDesk has stored for that end point. For a system which regularly polls FreshDesk, processing all of the data becomes cumbersome. As each record in FreshDesk has an Updated At field you could specify a Date/Time in your API call. The API would then only return the records which have been updated since the given date. For example:
domain_URL/contacts.xml?updated-at={datetime}
domain_URL/helpdesk/tickets.xml?updated-at={datetime}
The following examples show a given date raw and URL encoded:
domain_URL/helpdesk/time_sheets.xml?updated-at=2012-07-05T10:59:38
domain_URL/helpdesk/time_sheets.xml?updated-at=2012-07-05T10%3A59%3A38
Or a Unix Timestamp would work more easily:
domain_URL/helpdesk/time_sheets.xml?updated-at=1278327578
This would greatly reduce the amount of data transfer from FreshDesk to keep the data in an external system up to date.