Question: What's indexed piecewise used for?

The page ?type,piecewise shows the example

type(piecewise[](x < 1, a, b), 'piecewise');

and lines 4-8 of showstat(`print/piecewise`) deal with the case of an indexed piecewise. Yet I can find no other reference to indexed piecewise. What is it used for? When I put an index on a piecewise, nothing special seems to happen, either computationally or display-wise:

piecewise[abs](x > 0, x, -x);
piecewise[Carl](x > 0, x, -x);

The code in `print/piecewise` suggests that it serves some purpose.

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