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> Would other interventions (insulation on the pipes, say) improve these metrics at lower cost? We don't know.

There is a "Related Articles" section that goes into facets of the topic. This is published in Green Building Advisor, and the audience would have some knowledge about various aspects of building science and efficiency. The publication is not strictly aimed at home owners.

A lot of times by the time the designs get to a general contractor or plumber they're already fairly baked. The placement of various rooms (kitchen, bath, powder, laundry, etc) is one of the first orders of business, and it's an easy way to have designers/architects think of layout without getting into the plumbing details (home-run, race/speedway).

User training for this metric ends up being easy: draw a box, smaller is better. No need to get into things like plumbing architecture, materials, labour, etc.