They are sourcetype leftover examples of simpler times.
They can work on very generic datasets, but if you intend to ingest more specific logs, it's better to create new specific sourcetypes. (or use the ones provided by specific enterprise standard in their apps, and likely compatible with the Common Information Model).
The reason is that, if you all many of your events have the same sourcetype, then the day you want to setup a custom filters/field parsing/index time or search time processing, it will apply to a large set of data. While if you apply it to a specific sourcetype, you can control better the scope.
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