Note that SystemIndexer and SystemWorkIndexer will be in action in an upgraded system (not a fresh installation) till all indexes have been converted to Elastic Search. The user must explicitly re-index from the search landing page to create Elastic Search indices to get this conversion done. Till such time, search will be serviced by the older Apache Lucene library (used as the search library till 7.1.6) and SystemIndexer and SystemWorkIndexer are needed to keep those indices up to date.
In our case, we have upgraded to 7.1.7 an year back (last year & no more upgrades happened after that) . Please advise if these Agents (SystemIndexer and SystemWorkIndexer) can be safely disabled now ??