Layer styles are useful because of their parametric and their non-destructive natures.
Smart Filters are useful, but require the creation of a smart object beforehand.
I'd like to suggest new layer styles, of commonly used effects, that would help to automate time-consuming tasks.
Cast Shadow would simulate the shadow casted by a light placed in front or behind the object/layer.
It would use most of the controls found on the proposed Mirror layer style (point of origin, distance, angle, blurring, fade, shrinking, enlarging...)
I hope that other users will chime in with proposed refinements, or create other threads with additional (useful and feasible) layer styles they'd like to see.