If you plan to sync records, many [record].list endpoints support sync tokens (syncToken). This is an opaque token that is provided in the response or, for paginated lists, on the last page of results.
{
"success": true,
"results": [...],
"moreDataAvailable": false,
"syncToken": "Rld2D",
}
The next time you plan to sync, use the syncToken from your previous sync to only sync records that have changed since then.