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.
Mirror would create a reflection of the layer that fades with distance, it is commonly used in the products pictures of a famous computer/tablet/music player/phone manufacturer, and is even available as a Word art in Powerpoint! Another common name for that effect is "wet floor".
Proposed settings that one would be to be able to select: direction (bottom by default), angle of the reflection, starting point of the reflection (so that the object/layer can appear to be floating in the air above the reflecting surface) distance/curve of the fade, maybe an option to desaturate, lighten/darken, and/or blur with distance) There could also be an option to increase/decrease the width of the reflection. An additional eye candy would be to be able to distort the shadow with a map, for effects like waves, but we are way over in the cliché mode...
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. (see also cast shadow)