Autofield is useful in the creation of a workflow. Autofield consumes energy otherwise. The AutoField functionality could Automagically have a convert to SELECT functionality so that once the ideal metadata is constructed that a SELECT tool could replace the AutoField. Typically, when I autofield, I add a SELECT tool and then remove the autofield.
Another use case for Autofield is after reading in a CSV or after text to columns. Having a smart option for parsing avoids the need to use this particular tool.
Again, it is useful to have, just not useful to run on each workflow execution.
Cheers,
Mark