Losing symmetry is about the worst thing that can happen to a modeler.

Most modelers (check the youtube video's on how to model clothes for figures) Most modelers use the mirror function to build clothes.

Most modelers use the mirror function to build morphs for figures.
Or they check the "X" mirror to be sure the other side follows.
That is also why the "mirror" was added to the morph brush in Poser.

it cuts the workload in half.

But? When the figure is not symmetrical, all this becomes impossible.

Same goes for rigging, and Weight-and Bulge mapping.
Same goes for the fitting room when a rig is projected into the cloting.
Same goes for copy-left to right.

Losing symmetry in a figure is a nightmare for content creators.

Right up to the moment when the content creator WANTS to add non symmetrical items like buttons or folds, or uneven left-right items. Right up to that very last moment he/she will try to maintain symmetry at all cost.
But this is at the very-very last stage of the building process.

Lose symmetry in a figure, and basically you have lost the figure.
It takes twice the time to build for a non symmetrical figure.

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!