In order to plan the Incremental and Full Crawl scenarios and schedule , I’m adding the below information in this regard:
Note1: a full crawl should be done at least once before performing incremental crawl.
Note2: the above scenarios are covered for crawled content within SharePoint 2010/2013 farm, (not file shares , exchange public folders, custom connectors , etc… for those scenarios incremental crawl behavior might differ).
How about .SystemUpdate()? It seems like that one is only picked up by Full Crawl.