Just a couple of points to emphasize:

Asymmetrical morphs are fine. But, if that's all that is offered, it's terrible. :) Make a symmetrical version with asymetrical add-on morphs, if desired. That way, they can be pruned. Once you mess with a figure's symmetry, you are limiting the user's choices and capabilities with certain functions.

Facial asymmetry is the most noticeable, if one is aiming for realism. But, spacial relationships between facial features is what most people tend to notice. Use both when creating realistic morphs. A V4 face is almost immediately recognizable, no matter what morphs are on it, when spacial relationships are rigidly maintained.

Gross body asymmetry is rare. Small asymmetries will exist, but they're virtually meaningless - We're face people, we pay the most attention to faces. (No matter what bits people like to render the most...)

"Realism" in Poser has been discussed, ad nauseum. Poser figures, by default, are not scaled appropriately and are largely not intended to look "realistic." People "make do" with them and some can achieve some surprising results. But, the reason that these results are "surprising" is because... they're surprising. :)  Poser figs just aren't very realistic to begin with. (They can be made to get very close, though.)

The use of bump, displacement or normal maps can work wonders for establishing slight asymmetries, blemishes, creases, wrinkles, pockmarks, moles, whatever... Sometimes, a "geometry first" answer is not the best answer.