makes a product useful

Good design emphasizes the usefulness of a product whilst disregarding anything that could possibly detract from it.

A product is bought to be used. It has
to satisfy certain criteria, not only functional, but also psychological
and aesthetic.

MPZ 21 multipress citrus juicer, 1972, by Dieter Rams and
Jw├╝rgen Greubel for Braun.