Actually, Cheesehead, I'd say it's the reverse - reflectors shine, as it were, when you need to get a spread of light across an area, which produces a wide hotspot and wider corona with which one can scan a wide area. This produces quite a bit of usable light, though the amount is limited by the reflector's efficiency, as well as the lens... and all comes at the expense of throw.
A set of optics can collimate the light a lot more, like the TIROS (Total Internal Reflective Optical System) of the Inova T and XO-series lights, or the new KL1 from Surefire, which results in a smaller but more intense hotspot, and with most of the light collected by the optics for transmission across a specific distance. This increases throw substantially, which means you can get a lot more light on a given spot than you'd have with a reflector. It does, however, mean that you've got almost no corona and the angle of illumination is just a few degrees (10 degrees or less, from what I've seen). This is useful in spotlights, but useless when you're searching for things or need to navigate in the dark, because you'll miss a tree-branch that's just a foot ahead of you unless you shine the light at your feet (which is a waste of a light, IMO).
It depends on your needs and the purpose of the light - a lighthouse's light source uses a large Fresnell lens because they need to be able to project a tight beam across some distance, and a police spotlight has the same sort of lens for the same reason - to put a lot of light on a specific spot, which means the area is more intensely lit. If you're trying to make your way around in the dark, or have to do a lot of searching in a field or hilly area, a searcher will use a light with a lot of flood - while the overall intensity of light per unit of distance is less, they can scan a wider area in the process, and thus see things that they may have otherwise missed.
I don't know how you're measuring efficiency here - if you mean the amount of overall usable light... again, it depends on the situation. Do you need a more intense light on a specific point, or do you need a spread of light across an area? If you're looking at efficiency in terms of throw, a good reflector of sufficient size and good angles of reflection will do as well as an optic - but a smaller optic will throw as much, if not more light on the same spot, in a much smaller package. But while the optic may provide an intense spot of light, it may actually 'lose' more light in the material due to it being reflected back into the head of the flashlight than a properly designed reflector which will send nearly ALL the light shining out through the lens, where an optic may have enough internal reflection or material to 'damp out' some of the light you're trying to send out - you have to figure the refractive index of the material you're using in the optics as well.. and more material means more of that light is 'wasted', as it were, as it gets 'absorbed' or refracted by the optics into a non-usable form.
But that's just one man's opinion.