We're looking on enabling the indexing of the anonymous contacts in the xdb index, but the https://doc.sitecore.com/en/developers/91/sitecore-experience-platform/enable-indexing-of-anonymous-contacts-in-the-xdb-index.html page warns about the following:
Enabling this setting typically causes a significant increase in the amount of data to be indexed. Make sure that both Solr / Azure Cognitive Search and the xConnect Search Indexer are sized appropriately.
What is "sized appropriately"? Which setting is it referring to? Is it the ParallelizationDegree and BatchSize in the sc.Xdb.Collection.IndexerSettings.xml? What's a general approach to make sure that it's sized appropriately?