From the chapter “Smart IBL” on hdrlabs.com – “Another common problem is the sun. It’s just too bright, which makes it notoriously hard to capture. It’s even harder to render with, because it causes the worst render artifacts. Much more convenient is a regular 3d directional light, allowing more control over intensity and shadow. Such advanced lighting rigs result in better renderings in less render time, but they can be a pain to set up. Aside from preprocessing the HDR images the right way, you have to pull a dozen hidden levers in a 3d application to make it work. Even if you know exactly how to set up an advanced IBL rig, it becomes tedious and repetitive work.” (my boldface)
So it seems Smart IBL is a set of presets that do the “3D directional light[ing]” for you. All well and good if you want to surrender control of your lighting to a preset. But this seems to be exactly what I described above, using Environmental Lighting (Blender IBL process) to generate the illumination “presence” an environment can bring, plus direct Lamp lighting (with or without modulating imagery) for the directional modeling and shadows.
Thing about IBL as I understand it is that it does not really cast light rays as a Lamp does, originating at a source and impinging on a surface. Instead, it casts a “probe ray” (my terminology, not jargon) from an area on the IBL image (resolution dependent on the image and the Sampling settings) towards an illuminated object that determines how & where a pixel from the IBL source image will impinge on the object, then “colors” the surface accordingly using standard or HDR values. This is the form of raytracing used by IBL, but afaik it does not include calculation of cast shadows or explicit volume modeling based on light direction – it cannot, because it is in essence omni-directional (hence the term “global illumination” or GI), the rays being cast from all points in the “invisible sky” formed by the IBL image.
And I strongly disagree that using direct 3D lighting (i.e., Lamps in Blender) requires pulling “a dozen hidden levers” – this is sales pitch hyperbole in my opinion (not so humble, either). In many of my Env. Lighting setups (see again the Nezina renderings) I use only two lamps, one for direct sunlight (tinted and angled for time of day and surroundings, plus adjustments to shadow softness as appropriate) and one for specialized fill, such as bounce from beach sand or boosting the saturation of the green component in a dense forest scene. All the controls for such Lamps are present in a single panel in the Blender UI, not hidden, and while there are quite a few, maybe even a dozen, not all need be used all the time.
One of the reasons I learned how to use Env. Lighting in Blender is because it provides a much more naturalistic method of lighting the human figure (my spesheealitee) than traditional key & fill light setups, but as with any image-making situation, the scene determines the lighting requirements, so IBL becomes just another tool to choose, not the be-all and end-all of lighting solutions.
I’ve done both traditional film photography (many formats, studio & location)) and film-making (mainly 16mm), with all the lighting hassles that involves, and 3D lighting is much, much simpler, with a great deal of control over the situation that the real world isn’t polite enough to allow 
But like all disciplines, it must be learned to be used effectively. Or, you can rely on presets.
– there are a number of nudes) are affected.